Lewis Hamilton ended first practice for the Singapore Grand Prix atop the order in his Mercedes.
The Briton led the Red Bulls of Mark Webber and Sebastian Vettel in a tentative session that took a long time to get going as even backmarkers waited for track conditions to improve.
The majority of order changes at the front took place around the halfway point. In a busy few minutes, the early pace-setting Williams duo and McLaren's Sergio Perez were usurped as the Red Bulls and Mercedes took control.
Hamilton, Nico Rosberg and Webber swapped the top spot several times before Hamilton's 1m47.055s secured practice one honors. Webber was 0.365 second slower in second, with Vettel half a second further back but achieving his best time near the end of a long run.
Rosberg completed the top four ahead of Lotus team-mates Kimi Raikkonen and Romain Grosjean. The latter's running was limited by a steering problem. Fernando Alonso was the fastest Ferrari in seventh.
Perez fell back to eighth, six places ahead of McLaren team-mate Jenson Button, while Felipe Massa was also outside the top 10 in the second Ferrari in 12th as Toro Rosso's Jean-Eric Vergne and Sauber's improving rookie Esteban Gutierrez claimed ninth and 10th, with Pastor Maldonado's Williams 11th.
The 22 race drivers took part in the session, with no one standing aside for a reserve as teams preferred to maximize their lead racers' track time on the tricky Marina Bay street track.
Pos Driver Team Time Gap Laps
1. Lewis Hamilton Mercedes 1m47.055s 20
2. Mark Webber Red Bull-Renault 1m47.420s +0.365s 20
3. Sebastian Vettel Red Bull-Renault 1m47.885s +0.830s 19
4. Nico Rosberg Mercedes 1m48.239s +1.184s 23
5. Kimi Raikkonen Lotus-Renault 1m48.354s +1.299s 18
6. Romain Grosjean Lotus-Renault 1m48.355s +1.300s 12
7. Fernando Alonso Ferrari 1m48.362s +1.307s 21
8. Sergio Perez McLaren-Mercedes 1m49.267s +2.212s 20
9. Jean-Eric Vergne Toro Rosso-Ferrari 1m49.348s +2.293s 23
10. Esteban Gutierrez Sauber-Ferrari 1m49.355s +2.300s 21
11. Pastor Maldonado Williams-Renault 1m49.481s +2.426s 20
12. Felipe Massa Ferrari 1m49.493s +2.438s 16
13. Valtteri Bottas Williams-Renault 1m49.510s +2.455s 21
14. Jenson Button McLaren-Mercedes 1m49.608s +2.553s 20
15. Paul di Resta Force India-Mercedes 1m49.887s +2.832s 18
16. Adrian Sutil Force India-Mercedes 1m50.092s +3.037s 20
17. Nico Hulkenberg Sauber-Ferrari 1m50.222s +3.167s 17
18. Daniel Ricciardo Toro Rosso-Ferrari 1m50.757s +3.702s 16
19. Jules Bianchi Marussia-Cosworth 1m52.359s +5.304s 16
20. Max Chilton Marussia-Cosworth 1m52.673s +5.618s 15
21. Giedo van der Garde Caterham-Renault 1m52.920s +5.865s 24
22. Charles Pic Caterham-Renault 1m53.647s +6.592s 23