Red Bull's Mark Webber set the pace from Lotus's Kimi Raikkonen in first practice at the Malaysian Grand Prix.
The Australian was 0.068 seconds faster than Raikkonen, who won the first race of the season in Australia on Sunday.
Webber's team-mate Sebastian Vettel was third, ahead of Ferrari's Fernando Alonso and Mercedes' Nico Rosberg.
The leading runners appeared closely matched, with only 0.384secs separating Webber from Alonso. McLaren continued to struggle, with Jenson Button 11th.
Run in hot, humid conditions, the best part of half of the 90-minute session had passed before the drivers started to run seriously.
Mercedes driver Lewis Hamilton was the first big name to set a time, which was supplanted by Lotus's Romain Grosjean and Rosberg before Webber emerged to set the benchmark.
Webber, who was sixth in Australia after losing a front-row starting position following an electronics failure, was out at the same time as Vettel, and was slightly quicker.
Webber initially set a one minute 37.588, which Vettel followed with a 1:37.354, before Webber set his fastest lap of 1:36.395 and Vettel then a 1:37.104.
Impressively, Raikkonen set his best time on his first flying lap out of the pits after a delay while the team fixed a problem on the car.
Alonso, second in Australia, was one of the last to emerge from the pits for proper running but went fourth straight away.
The Spaniard's team-mate Felipe Massa was seventh fastest, 0.452secs off Alonso.
Massa was sandwiched by the Force Indias, Adrian Sutil sixth and Paul di Resta eighth.
Hamilton ended the session ninth after spending much of his time doing a race-simulation run on a heavy fuel load.
Grosjean rounded out the top 10 as Williams's Pastor Maldonado took 12th, ahead of the second McLaren of Sergio Perez.
Williams development driver Susie Wolff, in a role as BBC summariser, said: "The thing that stands out is that it is very similar to Melbourne. The Force India is fast and the Lotus, too. It wasn't a one-off that they were quick there."
It was immediately clear that tyre usage could be a decisive factor in Malaysia, as it was in Australia.
All the teams struggled to one degree or another with 'graining', where the surface of the tyre overheats and shreds.
BBC F1 analyst Gary Anderson said: "The two Mercedes cars were definitely using the rear tyre - there was a lot of graining on the rear tyre which is a tell-tale sign of a lot of wheelspin. That was one of their problems last year.
"Button's seemed to have cleaned up a little bit. Perhaps McLaren have now got a set-up on the car that does not deteriorate the tyres, which means they can work on the car a bit more."
First practice results:
1. Mark Webber (Aus), Red Bull - 1min 36.935secs
2. Kimi Raikkonen (Fin), Lotus - 1:37.003
3. Sebastian Vettel (Ger), Red Bull - 1:37.104
4. Fernando Alonso (Spa), Ferrari - 1:37.319
5. Nico Rosberg (Ger), Mercedes - 1:37.588
6. Adrian Sutil (Ger), Force India - 1:37.769
7. Felipe Massa (Brz), Ferrari - 1:37.771
8. Paul Di Resta (GB), Force India - 1:37.773
9. Lewis Hamilton (GB), Mercedes 1:37.840
10. Romain Grosjean (Fra), Lotus - 1:37.915
11. Jenson Button (GB), McLaren - 1:38.173
12. Pastor Maldonado (Ven), Williams - 1:38.673
13. Sergio Perez (Mex), McLaren - 1:38.830
14. Nico Hulkenberg (Ger), Sauber - 1:39.054
15. Esteban Gutierrez (Mex), Sauber - 1:39.204
16. Valtteri Bottas (Fin), Williams - 1:39.208
17. Jean-Eric Vergne (Fra), Toro Rosso - 1:39.284
18. Daniel Ricciardo (Aus), Toro Rosso - 1:39.567
19. Giedo van der Garde (Ned), Caterham - 1:40.728
20. Jules Bianchi (Fra), Marussia - 1:40.996
21. Charles Pic (Fra), Caterham - 1:41.163
22. Max Chilton (GB), Marussia - 1:41.513