Sebastian Vettel continued his run at the Circuit of the Americas, topping second practice despite missing half the session with a water leak.
Vettel picked up where he left off this morning, hitting the front almost immediately with a 1:40.7. However, after just three laps he headed back into the pits leaving it to his rivals to take control of the timesheets.
Lewis Hamilton was the next to lead the way followed by Mark Webber, Jenson Button, Fernando Alonso and Nico Rosberg. The Mercedes driver had the benchmark time down to a 1:40.096 after the first 15 minutes of practice, which saw everyone excluding Pedro de la Rosa and Narain Karthikeyan set a time in a busy start to second practice.
Drivers were still struggling to stay on the track with Felipe Massa running wide at Turn 19 and Hamilton using the run-off area surrounding the blind Turn One at the top of the hill.
With 30 minutes gone Rosberg was still in the P1 slot while Vettel was stuck in his garage as his Red Bull mechanics worked on his RB8, which had suffered a water cooling problem.
His team-mate Webber hit the front with a 1:39.485 and continued lapping, dropping the benchmark time to a 1:39.277 before he was overhauled by Massa.
Webber and Kimi Raikkonen were the first of the front-runners to head out on the medium Pirellis, both swapping over with 40 minutes remaining. Webber went quickest with a 1:38.958 and then even quicker on his second flying lap. Hamilton climbed to second ahead of Button while Vettel improved to fourth when he finally returned to the track for the final 25 minutes.
In what seemed like only a matter of time Vettel hit the front with a 1:37.718, 0.757s up on Webber. Alonso improved to third ahead of Hamilton and Button.
The final 10 minutes saw the drivers swap back to the white-marked Pirellis and with heavier fuel loads worked on race set-up. This meant Vettel finished the session unchallenged in the P1 slot.
01 Sebastian Vettel Red Bull 1:37.718 17 laps
02 Mark Webber Red Bull 1:38.475 0.757 36 laps
03 Fernando Alonso Ferrari 1:38.483 0.765 35 laps
04 Lewis Hamilton McLaren 1:38.748 1.030 31 laps
05 Jenson Button McLaren 1:38.786 1.068 32 laps
06 Felipe Massa Ferrari 1:39.029 1.311 33 laps
07 Nico Rosberg Mercedes 1:39.448 1.730 32 laps
08 Bruno Senna Williams 1:39.531 1.813 38 laps
09 Kamui Kobayashi Sauber 1:39.653 1.935 36 laps
10 Michael Schumacher Mercedes 1:40.115 2.397 30 laps
11 Kimi Raikkonen Lotus 1:40.166 2.448 32 laps
12 Pastor Maldonado Williams 1:40.230 2.512 35 laps
13 Romain Grosjean Lotus 1:40.286 2.568 32 laps
14 Sergio Perez Sauber 1:40.326 2.608 35 laps
15 Daniel Ricciardo Toro Rosso 1:40.435 2.717 30 laps
16 Jean-Eric Vergne Toro Rosso 1:40.516 2.798 32 laps
17 Nico Hulkenberg Force India 1:40.700 2.982 34 laps
18 Paul di Resta Force India 1:41.430 3.712 35 laps
19 Heikki Kovalainen Caterham 1:42.476 4.758 38 laps
20 Timo Glock Marussia 1:42.652 4.934 33 laps
21 Vitaly Petrov Caterham 1:42.846 5.128 38 laps
22 Charles Pic Marussia 1:43.538 5.820 38 laps
23 Pedro de la Rosa HRT 1:44.453 6.735 16 laps
24 Narain Karthikeyan HRT 1:45.114 7.396 20 laps
Practice Pictures From Austin