Lewis Hamilton set the early pace in the Malaysian Grand Prix weekend with the quickest time in the opening free practice session for Mercedes.
The Briton recorded his fastest time, a 1m40.691s lap, 0.152 seconds ahead of Ferrari's Kimi Raikkonen, an hour into the session, at the hot and humid Sepang International Circuit.
The first Formula 1 running early on Friday morning was characterised by a number of drivers struggling with rear grip and locking brakes on the dry and dusty circuit.
Fernando Alonso spun his Ferrari at the high-speed Turn 8 - a mistake repeated at the same corner by Williams's Felipe Massa. Hamilton went off at Turn 11 in the closing stages and the errors pointed to the general lack of grip at the tricky Sepang track.
A few teams suffered reliability problems in the blistering heat as they continued to adjust to their new 1.6-litre V6 power units.
McLaren's Keven Magnussen had just set the fastest time before the hour mark when his car came to a halt after losing engine power at the pitlane entrance. He set the fifth fastest time overall, just one place behind team-mate Jenson Button.
World champion Sebastian Vettel ended practice one in seventh place - 0.832s off Hamilton's quickest lap.
Lotus hit the most trouble as Romain Grosjean stopped out on track after just two laps of running with a problem with his MGU-H, while team-mate Pastor Maldonado spent most of the session in the garage.
He emerged from the pits less than 20 minutes from the end of practice only to suffer a smoky end to his first lap back out of the pits.
Rosberg ended up third fastest in his Mercedes, but the Australian Grand Prix winner radioed into his team with an early concern with his car after he locked the rear brakes and nearly spun while entering the pitlane after his installation lap right at the beginning of the practice period.
Practice benefited from the use of the additional bonus tyre in the first half and hour and during that time Alonso was initially fastest ahead of Magnussen.
Among other incidents, Caterham's Marcus Ericssion and Sauber's Adrian Sutil both looped their cars under braking for the final corner but continued unharmed.
Sergio Perez suffered problems with his Force India and after his installation lap failed to complete another lap of the session.
Pos Driver Team/Car Time Gap Laps 1. Lewis Hamilton Mercedes 1m40.691s 19 2. Kimi Raikkonen Ferrari 1m40.843s +0.152s 20 3. Nico Rosberg Mercedes 1m41.028s +0.337s 19 4. Jenson Button McLaren-Mercedes 1m41.111s +0.420s 20 5. Kevin Magnussen McLaren-Mercedes 1m41.274s +0.583s 18 6. Jean-Eric Vergne Toro Rosso-Renault 1m41.402s +0.711s 15 7. Sebastian Vettel Red Bull-Renault 1m41.523s +0.832s 9 8. Nico Hulkenberg Force India-Mercedes 1m41.642s +0.951s 19 9. Felipe Massa Williams-Mercedes 1m41.686s +0.995s 23 10. Valtteri Bottas Williams-Mercedes 1m41.830s +1.139s 22 11. Fernando Alonso Ferrari 1m41.923s +1.232s 14 12. Daniel Ricciardo Red Bull-Renault 1m42.117s +1.426s 20 13. Adrian Sutil Sauber-Ferrari 1m42.365s +1.674s 21 14. Daniil Kvyat Toro Rosso-Renault 1m42.869s +2.178s 21 15. Esteban Gutierrez Sauber-Ferrari 1m42.904s +2.213s 23 16. Jules Bianchi Marussia-Ferrari 1m43.825s +3.134s 18 17. Marcus Ericsson Caterham-Renault 1m45.775s +5.084s 24 18. Max Chilton Marussia-Ferrari 1m46.911s +6.220s 10 19. Kamui Kobayashi Caterham-Renault 1m51.180s +10.489s 5 20. Sergio Perez Force India-Mercedes 2 21. Pastor Maldonado Lotus-Renault 2 22. Romain Grosjean Lotus-Renault 4