18:55 Hello everyone and welcome back to AUTOSPORT Live for continuing coverage and rolling updates from the penultimate round of this year's FIA Formula one world championship - the United States Grand Prix from the all-new Circuit of the Americas.

Sebastian Vettel blazed a trail as the drivers got their first taste of the 5.513 km track near Austin, Texas this morning, setting a benchmark time of 1m38.125s. The German's sensational lap was 1.418s clear of Lewis Hamilton, with Fernando Alonso more than two seconds back in third spot.

Vettel storms clear in first Austin practice

The teams will now focus their attention on making both types of tyre work and running with a full fuel load in the latter stages, in preparation for Sunday's 56-lap race.

18:56 Conditions remain fine, dry and sunny around the circuit - if a little on the cool side. Air temperature is up towards today's high of 20 degrees Celsius, while a light north-easterly breeze continues.

18:57 Conditions were extremely slippery at the start of first practice, but grip - and laptimes - improved rapidly throughout the first 90 minutes of running.

Each driver had two sets of hard rubber to help get used to the challenging lyout, giving more action than the regular tyre-conserving in P1.

It was all hard compound rubber this morning, with teams looking forwards to exploring the medium tyres in the upcoming session.

18:57 Track temperature has climbed in the continuous sunshine to 30 Celsius, with a few minutes to go until the start of the session.

18:58 Ma Qing Hua makes way at HRT for Narain Karthikeyan. The Indian takes over his race car for the rest of the weekend.

18:59 Vettel is already strapped into his car and ready to go for a short run when the session begins.

18:59 The typical strategy at the start of second practice is for teams to send their drivers out for a short run of six to eight laps on the harder tyre.

0 min: The practice session is underway.

0 min: Jean-Eric Vergne gets proceedings underway in the Toro Rosso.

0 min: Raikkonen, Kobayashi and Perez join the early runners.

1 min: He is joined on-track by team-mate Ricciardo. Maldonado follows them out for an early run.

1 min: Senna and Webber head out to check the latest track conditions after the break.

1 min: Alonso kicks up the construction dust in the pitlane as he heads out in his Ferrari.

2 min: Hamilton and Button are also on track for an early run.

3 min: Vettel is also on track, with the early group already into a timed lap.

3 min: Vergne gets the ball rolling with a time of 1m49.781s.

4 min: Perez tops the early times with a 1m43.418s lap in his Sauber.

4 min: Schumacher is now on track for Mercedes, while Vettel comes through to start his first timed attempt of the afternoon.

4 min: Ricciardo moves into third spot, behind Perez and Raikkonen, with a time of 1m47.343s.

5 min: Webber's first effort is 1m43.854s and he is straight into second place in the Red Bull.

5 min: Maldonado's opening salvo puts him in sixth spot with a time of 1m48.678s.

6 min: Vettel is already on top of the timesheet with his first attempt - 1m40.790s - 2.3s up on the rest.

6 min: Ricciardo improves on his second timed lap and moves up into second spot behind Vettel, with 1m43.094s.

7 min: Button moves up to second fastest in the developing order with a 1m42.091s lap.

7 min: Heavy traffic in places with 21 drivers out there for an early run. Neither HRT driver is on track as yet.

7 min: Hamilton comes around in 1m41.593s, which is enough for second place but still some way off Vettel's best.

8 min: Vettel is straight back into the pits after an unusually short three-lap run at this stage of proceedings.

8 min: Grosjean ends his lap sixth fastest, with Raikkonen now seventh in his Lotus.

10 min: Vettel pitted due to an issue with the water system on his car. Usually, we'd expect drivers to complete six to eight laps on this run.

10 min: Button is the next to top the order with a 1m40.678s lap in his McLaren.

10 min: Webber comes through in 1m40.743s and moves up to second place, behind Button's McLaren.

11 min: Alonso, currently 12th, is now the fastest man in the sweeping first sector.

11 min: Di Resta logs an improvement and the Scot is up to 13th with a time of 1m43.180s.

11 min: Rosberg moves into second spot with a time of 1m40.723s.

12 min: Alonso puts his Ferrari on top in 1m40.431s.

12 min: Vettel remains in the car, while the Red Bull mechanics investigate the water system issue.

13 min: Hamilton comes around and is only 0.015s slower than the new benchmark.

13 min: Any loss of track time or shuffling of the planned programme could be critical as far as set-up time is concerned, so this is no meaningless issue for Red Bull.

14 min: Meantime, Rosberg shoots to the top of the pile with a lap of 1m40.096s in the Mercedes.

15 min: Webber is now second in the other RB8 with a time of 1m40.229s, ahead of Alonso third and Hamilton in fourth.

15 min: Rosberg finds another two-tenths of a second and extends his advantage with 1m39.842s, as Webber pits after eight laps.

16 min: Alonso is slowed by passing Kobayashi on his latest tour but remains third fastest on the timesheet.

17 min: Rosberg returns to the pits, completing a seven lap run. Team-mate Schumacher is on his eighth lap.

17 min: Massa makes use of the popular Turn 19 escape route, one of the first to do so this afternoon.

18 min: Schumacher also pits, ending an eight lap run to kick off his session. The German is down in 11th position, 1.708s down on his team-mate, who tops the list.

18 min: Hamilton, currently fourth fastest, doesn't get his McLaren slowed for the uphill Turn 1, taking to the run-off.

20 min: Vettel remains in the cockpit as Red Bull mechanics continue working on his car.

20 min: Massa clocks his best of the session so far to go sixth fastest.

21 min: HRT has opted to run a short programme with both cars this afternoon. Karthikeyan is now getting ready and slowly moving towards his car.

22 min: Hamilton pits his McLaren after a lengthy 11-lap opening to the session.

22 min: Toro Rosso drivers Ricciardo and Vergne are out on track to begin their second run.

23 min: Ricciardo is ninth in the classification after his first effort, while his French team-mate is further down the list in 16th.

24 min: Massa tops the final sector time with a 1m40.064s to go second fastest, just over two tenths off Rosberg's benchmark.

26 min: This is clearly a big job at Red Bull, with Vettel now out of the car and waiting while a longer investigation continues.

26 min: Adrian Newey looks less than impressed, as he contemplates a severe loss of track time for the championship leader.

27 min: Three laps only on the board for Vettel so far in this session, while his rival Alonso is well into a second run and gathering data.

28 min: A concerned look on Vettel's face as he stands in the middle of the garage, wondering when he can go out and play again.

29 min: Vergne has improved on his second run and is up to 10th, with a time of 1m41.287s. He is one-tenth shy of his team-mate.

30 min: Raikkonen improves his time to a 1m40.830s, just under a second off the leading pace.

30 min: Grosjean complains that the rear of his Lotus is "all over the place"

31 min: Rosberg, Webber and Schumacher are on track for their second run, while Vettel's car is up on stands in bits and being worked on.

31 min: Replays pick up Grosjean in a massive sideways moment at Turn 19, explaining his radio message.

32 min: Meanwhile, Raikkonen has moved up to third fastest witha 1m40.166s lap.

32 min: Button is the next to improve with the fastest final sector, going second fastest and just fractions off the Rosberg benchmark.

33 min: Vergne improves again. He is doing well on this run and jumps up to ninth with 1m40.516s, ahead of Vettel and team-mate Ricciardo.

33 min: Alonso wobbles his way through Turn 19, which continues to prove difficult for the drivers.

34 min: Red Bull clearly has the speed though, as Webber demonstrates as he tops the list with a time of 1m39.485s.

35 min: Petrov has a spin at Turn 1 but escapes without too much drama in his Caterham.

35 min: Alonso moves up to second fastest, just five thousandths slower than Webber's new best.

36 min: Vergne is back in after the completion of a seven lap run in the Toro Rosso. He remains in ninth spot.

37 min: Meantime, work continues on Vettel's car. Red Bull needs to get this water leak resolved soon, or his long run strategy will be at risk later.

37 min: Hamilton is told to do a hard outlap as he equates his tyres to ice cubes.

38 min: Schumacher is back into the pits after a short four lap run in the Mercedes. He is down in 13th position, just over two seconds off the pace.

39 min: Medium compound rubber beginning to see action now as Petrov, Kovalainen and Pic test the softer tyres.

39 min: Webber is a quarter of a second up on his own benchmark after two sectors and looking to gain further time on the rest of the field.

39 min: Yes, the Australian does improve by two-tenths and comes through in 1m39.277s.

40 min: Karthikeyan is now on track for HRT and working through his first timed lap of the weekend.

41 min: Senna delivers a slight improvement and moves into 14th quickest with a time of 1m41.583s.

41 min: Webber returns to the pits, completing another eight lap run and gathering crucial data for Red Bull, given Vettel's problems.

42 min: Webber is 0.213s clear of Alonso in second, with Rosberg third, Button fourth and Massa in fifth spot.

42 min: Hamilton is eighth fastest at the moment and not looking entirely comfortable with his hard-shod McLaren at the moment.

42 min: Vettel has slipped down to 10th in the classification. He is now more than one-and-a-half seconds down on the benchmark time.

43 min: Karthikeyan is finally on the board with 1m56.701s. Team-mate de la Rosa is on the circuit for his first lap.

44 min: Massa again tops the final part of the lap to go third fastest in 1m39.710s.

45 min: Hamilton loses the rear of his McLaren and is clearly struggling for grip at the moment. He has pitted after recovering from the spin.

45 min: Massa continues his progress, clocking 1m39.106s to top the times.

45 min: Di Resta and Hulkenberg are back on track to begin their third run of the afternoon. They are down in 15th and 16th positions.

46 min: That's an improving long run for Massa, finding pace as the fuel load burns down on his hard compound rubber.

46 min: Medium compound tyres for di Resta on this run, as he looks to make a jump up the order.

47 min: Grosjean is next to try the switch to the medium compound.

47 min: Vergne and Hulkenberg are also on track using the medium Pirelli compound, as di Resta comes through with no improvement.

47 min: Massa finds a fraction more for a new best of 1m39.061s.

49 min: Vergne is slip-sliding all over the place on his medium compound tyres and early impressions are that we are again looking at three or four laps before the performance comes in.

49 min: Grosjean is slowed on his medium tyre effort as he encounters Karthikeyan in the HRT.

50 min: De la Rosa is off at Turn 8 but the Spaniard is able to continue, after losing around 13 seconds.

50 min: No improvement for Vergne on his first timed lap either on the option tyre. Meantime, di Resta is much quicker now on his third attempt.

51 min: Grosjean recovers from that delay with the fastest first sector on his medium rubber.

51 min: Di Resta finds three-tenths of a second with a lap of 1m41.442s and moves up to 14th position.

52 min: Spanners out at Sauber as well with mechanics looking at the exhaust on Kobayashi's Ferrari engine.

52 min: A bigger improvement for Force India team-mate Hulkenberg. He moves up to 11th with a time of 1m40.727s.

52 min: No improvement for Grosjean after backing out of that flying attempt, while Raikkonen is also now out on mediums.

53 min: Movement at Red Bull, as Vettel puts his balaclava on and begins to move towards his car, as the mechanics finish off repairs to the water system.

53 min: More good news for the championship leading team, as Webber shoots to the top of the list with a lap of 1m38.958s.

54 min: Vettel's car is back down at ground level and the German climbs aboard. He is being strapped in.

55 min: Rosberg is out there on his medium tyre run now. Maldonado has been off-track at Turn 19 but the Williams driver was able to continue.

55 min: Button heads out on medium compound rubber while Hamilton also has the option tyres fitted as he leaves the garage.

56 min: Karthikeyan has also been off at that tricky part of the circuit towards the end of the lap. He was similarly able to get going again.

56 min: Grosjean pits, reporting that his Lotus is "difficult to drive" after an outing on the medium compound.

57 min: Webber finds half-a-second and retakes the top position with a time of 1m38.475s on medium compound tyres.

58 min: Many drivers still not finding huge leaps with the medium rubber, struggling to get temperature in the Pirellis on a cold day.

59 min: Webber is beginning to fly now on his medium compound tyres. He posts the fastest first sector of all, but loses a little time in the middle section.

60 min: Schumacher leaps up the order and into sixth position with a lap of 1m40.115s.

60 min: Hamilton looks to be happier with his McLaren on the option tyres, improving to fourth fastest in 1m39.396s.

61 min: Senna improves to 15th with a lap of 1m41.214s. Vettel still not out yet.

61 min: Webber gets into a brief on-track altercation with Vitaly Petrov in the Caterham. The Australian squeezes through without contact and continued on his way to the pits.

62 min: So Webber is in after a seven lap run in the RB8, as Vettel joins the racetrack.

62 min: Kovalainen is touring with a left rear puncture on his Caterham.

63 min: Kovalainen makes it back to the pits after coming out worse in that contact with Vergne.

63 min: Vettel is now into a timed lap - only his second of the day.

64 min: Meanwhile, Hamilton is up to second fastest in 1m32.748s.

64 min: Button is also finding pace after several laps on the medium rubber, going third fastest in 1m38.786s.

64 min: Vettel comes round and completes his timed lap in 1m38.894s and moves into fourth position.

65 min: Hamilton has followed up his quick lap with an adventure at Turn 12.

65 min: Rosberg also improves on medium compound tyres and is seventh with a time of 1m39.448s.

66 min: Vettel has backed off a little on his second timed lap. He crosses the line and goes again.

66 min: Race control advises that the track is now clear in Turn 19, with marshals having had the slippery surface flags out for debris.

67 min: Massa has a wobble in the Silverstone-like sweepers at Turn 5. These ones, however, have handy painted asphalt instead of grass.

67 min: Rosberg is in after a seven lap run on the medium compound tyre.

68 min: Senna has also improved to eighth position in the Williams, with a lap of 1m39.531s. He is some way clear of team-mate Maldonado, who has just left the pits.

69 min: Hamilton now tops the middle sector as he finds more on a long run with the options. He's into the pits now, however.

70 min: Vettel much quicker on his fourth timed lap now but he has had to negotiate his way past Pic in the Marussia.

70 min: Alonso clocks a 1m38.483s to go third fastest during a run on the medium rubber.

70 min: Nevertheless, Vettel is still able to go quickest of all with a time of 1m37.718s.

71 min: Vettel is 0.757s clear of team-mate Webber, with Alonso just a shade slower in third spot, Hamilton fourth and Button fifth.

71 min: Vettel is back into the pits after a six lap run in the Red Bull.

72 min: Into the pits for the Ferrari pair as well with both being turned around for the final long run.

73 min: Webber is two laps into his long run. He asks on the radio if the team can check the data from the rear of the car, as he is feeling low grip.

73 min: Webber is told that they can't see anything obvious at this stage. He continues out there.

74 min: A spin for Grosjean before he returned to the Lotus pit, looping the car around at Turn 1.

75 min: Vergne has just joined the track to begin his long run. He is reminded of the clutch and engine modes that the team would like him to use on the radio.

76 min: Massa is back on track for a final run with medium rubber, advised on the radio how to brake for Turn 1... which ends in a smoky lock-up.

76 min: Rosberg and Schumacher are on track for their final run with less than 14 minutes of the session remaining.

78 min: Runs of three and six laps for Vettel so far. He hasn't started a high fuel run yet.

78 min: Long runs kicking in for many now, somewhat later than usual after extra time spent learning the track.

79 min: Vettel exits the garage now to begin his final run with around 11 minutes left on the clock.

80 min: Heavy traffic now with all 24 drivers on track, gathering important high fuel data for Sunday's 56-lap race.

81 min: Hamilton is told the plan is five timed laps on this late run.

82 min: Alonso tries a new line over the astroturf at Turn 19 before a quick pitstop.

83 min: Mid 1m45s race pace for the McLaren pair as they test the durability of the softer tyres.

84 min: Vettel comes through in a time of 1m45.721s, which is close to the McLaren pair in their current configuration.

85 min: Kobayashi, who is behind schedule after earlier exhaust strife, improves his best to a 1m40.000s to go ninth fastest, despite a lockup.

86 min: Pace improving into the 1m44s bracket now at McLaren, with durability looking good on these softer tyres.

87 min: "This pace looks good," Hamilton is told as he clocks a 1m44.196s lap.

89 min: Massa is told to "call it a day" by engineer Rob Smedley and duly pits his Ferrari.

89 min: Vettel locks up at Turn 12 as he continues to try and find a solid race pace. He continues after a brief run over the extra asphalt run-off area.

20:30 A puff of smoke through Turn 19 from Maldonado's Williams and he tours slowly into the pits.

20:30 The flag is out on the first day of practice at Austin.

20:30 A small fire ensues and Maldonado is instructed to switch off the car immediately.

20:31 He rolls towards the Williams garage and the mechanics take over, as they push the car the rest of the way.

20:31 Replays show flame coming from the right hand outlet as he toured into the pitlane entrance.

20:32 A fiery end to practice but it is Sebastian Vettel who again tops the times with 1m37.718s, 0.757s ahead of team-mate Mark Webber.

20:33 Alonso ends the day in third spot, keeping the pressure on the two RB8s, with Hamilton fourth ahead of McLaren team-mate Jenson Button.

20:34 Massa was sixth in the other Ferrari, with Rosberg seventh, Senna eighth, Kobayashi ninth and Schumacher rounds out the top 10.

20:35 Other notables: Raikkonen ends his day in 11th spot and one-tenth ahead of Lotus team-mate Romain Grosjean.

20:36 Problems for the Red Bull duo but they are one-two at the end of Friday practice. Join us tomorrow for final practice and qualifying.