Red Bull's Sebastian Vettel set the quickest time in the second Friday practice session under the lights in Singapore.
The German – who is still clinging to his remote title hopes – beat Fernando Alonso by 0.274sec, as the two-time champion gave his under-fire Renault team some encouragement with second place.
Heikki Kovalainen (McLaren) and Nick Heidfeld (BMW) were third and fourth ahead of championship leader Jenson Button's Brawn.
Mark Webber had been fastest for Red Bull as the early runs came to an end, but he had to sit out the second half of the session after spinning on the exit of the final corner.
The Red Bull crunched into the opposite wall and sustained significant left-side damage, causing a nine-minute stoppage and ending Webber's day.
Heidfeld knocked Webber off the top spot as soon as running resumed following the red flag, and the BMW driver stayed on top until everyone switched to super-soft tires in the closing minutes.
The usual flurry of late changes saw first Kovalainen, then Vettel move to the top of the standings – although Button and Lewis Hamilton set sector times that hinted at big improvements, only to hit traffic on their best laps.
Alonso had the same problem, losing a lot of time behind Jarno Trulli's Toyota on the penultimate lap of the day, but he made up for it by jumping to second next time around. Webber, surprisingly, remained sixth despite his crash, ahead of Nico Rosberg's Williams and Timo Glock's Toyota.
Practice one pace-setter Rubens Barrichello was only 11th in the second Brawn this time.
Giancarlo Fisichella had a quiet practice day for Ferrari, ending up 16th, but he was at least closer to his teammate Kimi Raikkonen, who was 0.3sec and two places ahead.
Romain Grosjean missed the early part of the session as repairs were completed following his crash in first practice, and only managed 19th.
Pos Driver Team Time Laps
1. Vettel Red Bull-Renault (B) 1:48.650 31
2. Alonso Renault (B) 1:48.924 + 0.274 27
3. Kovalainen McLaren-Mercedes (B) 1:48.952 + 0.302 30
4. Heidfeld BMW-Sauber (B) 1:49.098 + 0.448 31
5. Button Brawn-Mercedes (B) 1:49.311 + 0.661 34
6. Webber Red Bull-Renault (B) 1:49.317 + 0.667 14
7. Rosberg Williams-Toyota (B) 1:49.333 + 0.683 33
8. Glock Toyota (B) 1:49.342 + 0.692 30
9. Hamilton McLaren-Mercedes (B) 1:49.358 + 0.708 28
10. Kubica BMW-Sauber (B) 1:49.609 + 0.959 24
11. Barrichello Brawn-Mercedes (B) 1:49.616 + 0.966 30
12. Sutil Force India-Mercedes (B) 1:49.710 + 1.060 31
13. Trulli Toyota (B) 1:49.795 + 1.145 29
14. Raikkonen Ferrari (B) 1:49.941 + 1.291 29
15. Nakajima Williams-Toyota (B) 1:50.023 + 1.373 34
16. Fisichella Ferrari (B) 1:50.253 + 1.603 31
17. Buemi Toro Rosso-Ferrari (B) 1:50.527 + 1.877 29
18. Liuzzi Force India-Mercedes (B) 1:50.605 + 1.955 28
19. Grosjean Renault (B) 1:50.972 + 2.322 17
20. Alguersuari Toro Rosso-Ferrari (B) 1:51.423 + 2.773 31
All Timing Unofficial