Lewis Hamilton set the fastest time in opening practice for the Malaysian Grand Prix, but a last gap run to second by Mercedes' Nico Rosberg denied McLaren a likely one-two in the sesssion.
After a low-key opening to the morning, with the small teams monopolising the early track time, McLaren's Hamilton and Jenson Button moved into first and second around the session's halfway mark, before - like most of its rivals - focusing on heavier fuel runs later in the morning.
Their positions looked set going into the closing moments, until Rosberg slipped through with a lap 0.185 seconds off Hamilton's pace just after the chequered flag to split the McLarens.
Michael Schumacher was fourth in the second Mercedes. The former champion did not set a flying lap at all until just over the one hour mark while Mercedes worked on the rear of his car, but once on track Schumacher was rapid and quickly worked his way up to third, which became fourth when Rosberg jumped up the order.
Renault's Robert Kubica briefly led the way prior to the McLarens' mid-session surge and ended up fifth, ahead of Red Bull's Mark Webber, Force India's Adrian Sutil, and championship leader Fernando Alonso (Ferrari) in eighth.
Sebastian Vettel was only ninth for Red Bull, and at one stage reported issues with slowing the car down. But he did set the fastest sector two time of the morning on his in-lap after the flag. Sebastien Buemi completed the top ten for Toro Rosso.
Felipe Massa made two trips through the gravel and was 11th for Ferrari. Also in trouble were Toro Rosso's Jaime Alguersuari, who lost time to an electrical problem but recovered to 13th after repairs, and Sauber's Pedro de la Rosa. Like Massa, the Spaniard skittered through the Turn 12 gravel at speed but rejoined without damage.
Lotus test driver Fairuz Fauzy did a solid job on his first appearance in a GP weekend session. The Malaysian had a half-spin and brief trip over the grass, but was within half a second of team-mate Jarno Trulli until the Italian improved late on, and ultimately took 22nd. Force India's Paul di Resta, the other reserve driver in action, was 15th.
Pos Driver Team Time Laps 1. Hamilton McLaren-Mercedes 1:34.921 19 2. Rosberg Mercedes 1:35.106 + 0.185 19 3. Button McLaren-Mercedes 1:35.207 + 0.286 25 4. Schumacher Mercedes 1:35.225 + 0.304 14 5. Kubica Renault 1:35.402 + 0.481 22 6. Webber Red Bull-Renault 1:35.479 + 0.558 22 7. Sutil Force India-Mercedes 1:35.955 + 1.034 20 8. Alonso Ferrari 1:35.959 + 1.038 20 9. Vettel Red Bull-Renault 1:35.043 + 1.122 19 10. Buemi Toro Rosso-Ferrari 1:36.100 + 1.179 20 11. Massa Ferrari 1:36.451 + 1.530 22 12. Kobayashi Sauber-Ferrari 1:36.503 + 1.582 28 13. Alguersuari Toro Rosso-Ferrari 1:36.645 + 1.724 18 14. Petrov Renault 1:36.712 + 1.791 9 15. di Resta Force India-Mercedes 1:36.891 + 1.970 25 16. de la Rosa Sauber-Ferrari 1:36.899 + 1.978 24 17. Hulkenberg Williams-Cosworth 1:37.802 + 2.881 27 18. Barrichello Williams-Cosworth 1:38.278 + 3.357 18 19. Trulli Lotus-Cosworth 1:39.460 + 4.539 21 20. Glock Virgin-Cosworth 1:39.755 + 4.834 17 21. di Grassi Virgin-Cosworth 1:40.159 + 5.238 25 22. Fauzy Lotus-Cosworth 1:40.721 + 5.800 19 23. Senna HRT-Cosworth 1:41.832 + 6.911 27 24. Chandhok HRT-Cosworth 1:41.966 + 7.045 24 All Timing Unofficial