US GP: Vettel quickest again in second practice despite problems

The world champion had to park in the garage after just three laps at the start of the afternoon when the team detected the water system fault.

Vettel would not reappear for almost an hour, but when he did, he left his rivals in no doubt whatsoever about his pace this weekend as a 1m37.718s lap on his second medium-tyre run put him 0.757 seconds clear of the pack.

Even during Vettel's absence, Red Bull had been in front for most of the session thanks to Mark Webber.

The Australian had produced a 1m39.485s on hard tyres just after the half-hour mark to depose early pacesetter Nico Rosberg's Mercedes, and then found another two tenths next time round.

Felipe Massa enjoyed a seven-minute spell in first place when he delivered a 1m39.106s, but soon after Webber switched to the softer Pirellis and regained the top spot.

Webber's first medium-tyre effort was a 1m38.958s, and he swiftly improved to 1m38.475s - although that was firmly eclipsed by Vettel's pace when the German was back in action.

There was some cause for optimism for Vettel's title rival Fernando Alonso's Ferrari team. Alonso took third, just 0.008s down on Webber, and Massa had at least ended up quickest in the 'hard tyre' segment of the session.

The McLarens completed the top five, Lewis Hamilton escaping a Turn 13 spin to pip team-mate Jenson Button.

Sometime pacesetters Massa and Rosberg ended up sixth and seventh.

Bruno Senna was top Williams driver in eighth, while his team-mate Pastor Maldonado suffered an apparent engine problem in the closing seconds.

Kamui Kobayashi lost a lot of track time to an exhaust problem before taking his Sauber to ninth ahead of Michael Schumacher's Mercedes.

The Lotus duo were just outside the top 10. Romain Grosjean tested the limits of the dramatic Turn 1 with a quick spin late on, emulating an earlier error by Caterham driver Vitaly Petrov.

The other Caterham also had an incident. Heikki Kovalainen had to nurse his car around a full lap with a puncture following a light brush with Jean-Eric Vergne's Toro Rosso, which sustained front wing damage in the tangle.

At the tail of the field, the troubled HRT team did not leave the garage for the first half of the session and completed significantly less mileage than most of the pack.

Pos Driver                Team                  Time                Laps
 1. Sebastian Vettel      Red Bull-Renault      1m37.718s            17
 2. Mark Webber           Red Bull-Renault      1m38.475s  + 0.757   36
 3. Fernando Alonso       Ferrari               1m38.483s  + 0.765   35
 4. Lewis Hamilton        McLaren-Mercedes      1m38.748s  + 1.030   31
 5. Jenson Button         McLaren-Mercedes      1m38.786s  + 1.068   32
 6. Felipe Massa          Ferrari               1m39.029s  + 1.311   33
 7. Nico Rosberg          Mercedes              1m39.448s  + 1.730   32
 8. Bruno Senna           Williams-Renault      1m39.531s  + 1.813   38
 9. Kamui Kobayashi       Sauber-Ferrari        1m39.653s  + 1.935   36
10. Michael Schumacher    Mercedes              1m40.115s  + 2.397   30
11. Kimi Raikkonen        Lotus-Renault         1m40.166s  + 2.448   32
12. Pastor Maldonado      Williams-Renault      1m40.230s  + 2.512   35
13. Romain Grosjean       Lotus-Renault         1m40.286s  + 2.568   32
14. Sergio Perez          Sauber-Ferrari        1m40.326s  + 2.608   35
15. Daniel Ricciardo      Toro Rosso-Ferrari    1m40.435s  + 2.717   30
16. Jean-Eric Vergne      Toro Rosso-Ferrari    1m40.516s  + 2.798   32
17. Nico Hulkenberg       Force India-Mercedes  1m40.700s  + 2.982   34
18. Paul di Resta         Force India-Mercedes  1m41.430s  + 3.712   35
19. Heikki Kovalainen     Caterham-Renault      1m42.476s  + 4.758   38
20. Timo Glock            Marussia-Cosworth     1m42.652s  + 4.934   33
21. Vitaly Petrov         Caterham-Renault      1m42.846s  + 5.128   38
22. Charles Pic           Marussia-Cosworth     1m43.538s  + 5.820   38
23. Pedro de la Rosa      HRT-Cosworth          1m44.453s  + 6.735   16
24. Narain Karthikeyan    HRT-Cosworth          1m45.114s  + 7.396   20