Sebastian Vettel was quickest in second practice in Singapore, completing a strong start to the weekend that could see him crowned world champion for the second straight year.
The Red Bull driver set the early practice two pace with a 1m47.375s lap - 0.7 seconds ahead of team-mate Mark Webber as the champion squad dominated the initial running.
Those times stood until drivers began switching to super-soft tyres in the second half of the session. Ferrari's Felipe Massa was the first of the frontrunners to do so and clocked a 1m47.120s to go quickest with 41 minutes to go. His team-mate Fernando Alonso then beat that time by 0.6s 10 minutes later to hit the front.
Vettel backed off on his first super-soft lap when he encountered Timo Glock's Virgin, but his second attempt resulted in a 1m46.374s, putting him on top by 0.201s over Alonso. With the top teams all switching to long runs thereafter, Vettel's position was secure.
Lewis Hamilton took third for McLaren, while his team-mate Jenson Button's evening ended very early when he slid straight on at Turn 14 just before the session's halfway point. Although Button stopped without hitting the barriers, he was unable to make his car reverse back on course, so had to abandon the McLaren. He tumbled to 10th in the times as a result.
Massa was pushed back to fourth in the end, just ahead of Mark Webber in the second Red Bull.
Michael Schumacher's strong recent run continued with sixth place for Mercedes, followed by Adrian Sutil's Force India and the Saubers of Sergio Perez and Kamui Kobayashi. The latter enlivened the evening with a wild misjudging of the Turn 10 chicane that resulted in the Sauber flying through the air over the middle kerb.
A tough night for Toro Rosso saw Jaime Alguersuari sidelined in the garage with a mechanical issue after 14 laps, though his time before then was still good enough for 11th, and Sebastien Buemi derange his suspension when he made firm contact with the wall at the penultimate corner.
Schumacher also hit the barriers, in his case at Turn 3, as he almost spun the Mercedes on an early run. But the wall nudged the car back onto the correct line and Schumacher continued without damage.
Paul di Resta spent most of the session in the pits while Force India attended to a time-consuming issue on his car. He got back out with a few minutes to go, and was able to lift himself from 17th to 13th.
Pos Driver Team Time Laps 1. Sebastian Vettel Red Bull-Renault 1m46.374s 33 2. Fernando Alonso Ferrari 1m46.575s + 0.201 28 3. Lewis Hamilton McLaren-Mercedes 1m47.115s + 0.741 22 4. Felipe Massa Ferrari 1m47.120s + 0.746 23 5. Mark Webber Red Bull-Renault 1m47.265s + 0.891 28 6. Michael Schumacher Mercedes 1m48.418s + 2.044 27 7. Adrian Sutil Force India-Mercedes 1m48.866s + 2.492 32 8. Sergio Perez Sauber-Ferrari 1m49.578s + 3.204 27 9. Kamui Kobayashi Sauber-Ferrari 1m49.730s + 3.356 29 10. Jenson Button McLaren-Mercedes 1m49.751s + 3.377 10 11. Jaime Alguersuari Toro Rosso-Ferrari 1m49.792s + 3.418 14 12. Bruno Senna Renault 1m50.241s + 3.867 31 13. Paul di Resta Force India-Mercedes 1m50.345s + 3.971 8 14. Vitaly Petrov Renault 1m50.399s + 4.025 29 15. Nico Rosberg Mercedes 1m50.790s + 4.416 28 16. Rubens Barrichello Williams-Cosworth 1m50.897s + 4.523 24 17. Pastor Maldonado Williams-Cosworth 1m50.937s + 4.563 30 18. Heikki Kovalainen Lotus-Renault 1m51.950s + 5.576 26 19. Sebastien Buemi Toro Rosso-Ferrari 1m52.257s + 5.883 15 20. Jarno Trulli Lotus-Renault 1m52.489s + 6.115 25 21. Timo Glock Virgin-Cosworth 1m53.579s + 7.205 25 22. Jerome D'Ambrosio Virgin-Cosworth 1m54.649s + 8.275 25 23. Daniel Ricciardo HRT-Cosworth 1m54.754s + 8.380 29 24. Tonio Liuzzi HRT-Cosworth 1m55.198s + 8.824 26 All Timing Unofficial