Fernando Alonso sprung a surprise in second practice for the Singapore Grand Prix, beating Lewis Hamilton to the fastest time in the closing seconds of the session.
The Renault driver outpaced the McLaren by 0.098 seconds, with Ferrari's Felipe Massa and McLaren's Heikki Kovalainen third and fourth, and Nico Rosberg impressing again for Williams in fifth.
Hamilton was quickest for the majority of the session, swiftly moving ahead of early pacesetter Rosberg and then chipping away at his time for the next hour and steadily edging further ahead.
Massa, who took a couple of detours down escape roads without damage, usurped the McLaren with 15 minutes remaining, with Hamilton's teammate Kovalainen then pushing the Briton down to third as he lapped just 0.004 seconds slower than Massa.
It didn't take long for Hamilton to respond, though, as he switched to the softer tyres for the last few minutes and lapped in 1:45.752, beating Massa by 0.041 seconds.
Until Alonso's late lap, it looked like Hamilton was set to remain on top. But the Renault produced a 1:45.654 just before the chequered flag, after a spectacular lap on the super-soft tyres.
However Hamilton's practice one benchmark of 1:45.518 would remain the fastest lap of the day - demonstrating how quickly the teams and drivers had got to grips with the circuit, and that the track had offered competitive conditions right from the outset rather than first practice being spent cleaning a dusty surface.
Behind the top four, Rosberg was on the pace throughout the session again and took fifth, ahead of BMW's Robert Kubica. Kimi Raikkonen only managed seventh in the second Ferrari, with Jenson Button also continuing his promising earlier form to take eighth for Honda.
The session was less eventful than opening practice, although Timo Glock lost his Toyota's front wing when he spun into the wall exiting Turn 7 right at the end.
There was also an eyebrow-raising moment at the first corner when Sebastien Bourdais exited the pitlane just as Nick Heidfeld committed to the first turn on a flying lap, causing the Toro Rosso to cut across the inside run-off and the BMW to take to the extra asphalt on the opposite side of the track.
The unusually short one-hour gap between first and second practice almost caught the organisers out, as the session start was delayed by two minutes while Paddock Club guests were cleared from the pitlane.
The unique schedule was also bad news for Mark Webber and Red Bull, denying the team much-needed time to repair the damage sustained in the Australian's earlier crash. Webber finally joined the track with 27 minutes to go, and after initially languishing at the foot of the times, he leapt up to 11th on his last lap.
Force India's Giancarlo Fisichella was also in trouble. The Italian was on the cusp of the top ten at first, only for a gearbox problem to sideline him for the second half of the session, leaving him 17th.
Pos Driver Team Time Laps 1. Alonso Renault (B) 1:45.654 30 2. Hamilton McLaren-Mercedes (B) 1:45.752 + 0.098 28 3. Massa Ferrari (B) 1:45.793 + 0.139 31 4. Kovalainen McLaren-Mercedes (B) 1:45.797 + 0.143 31 5. Rosberg Williams-Toyota (B) 1:46.164 + 0.510 34 6. Kubica BMW Sauber (B) 1:46.384 + 0.730 36 7. Raikkonen Ferrari (B) 1:46.580 + 0.926 25 8. Button Honda (B) 1:46.901 + 1.247 32 9. Nakajima Williams-Toyota (B) 1:47.013 + 1.359 32 10. Glock Toyota (B) 1:47.046 + 1.392 22 11. Webber Red Bull-Renault (B) 1:47.137 + 1.483 15 12. Piquet Renault (B) 1:47.145 + 1.491 35 13. Vettel Toro Rosso-Ferrari (B) 1:47.300 + 1.646 33 14. Bourdais Toro Rosso-Ferrari (B) 1:47.487 + 1.833 24 15. Coulthard Red Bull-Renault (B) 1:47.640 + 1.986 31 16. Heidfeld BMW Sauber (B) 1:47.760 + 2.106 36 17. Fisichella Force India-Ferrari (B) 1:47.965 + 2.311 12 18. Barrichello Honda (B) 1:48.009 + 2.355 25 19. Trulli Toyota (B) 1:48.059 + 2.405 28 20. Sutil Force India-Ferrari (B) 1:48.311 + 2.657 36 All Timing Unofficial