World championship leader Nico Rosberg set the pace in a Practice One session for the Malaysia GP overshadowed by the Renault car of Kevin Magnussen catching fire.
The Renault burst aflame as it returned to the team's garage with Magnussen forced to leap out of the car as flames engulfed the RS16.
"We had a fuel leak from a breather and we were running some experimental parts for Mexico," Renault technical chief Nick Chester told Sky F1. "But everyone is ok and that's the main thing. Fortunately the car doesn't seem to be too badly damaged."
When the session resumed, it was Rosberg, who has won the last three races to take the lead of the championship, who set the pace on soft tyres. The German's benchmark lap of 1:35.227 was almost half a second faster than the best of Lewis Hamilton. However, Hamilton's fastest time was set on the slower medium compound.
Mercedes' one-two at the top of the timesheets was their 10th in the last eleven Practice One outings although both Rosberg and Hamilton ran off the track during the session as they explored the limits of the relaid track.
Despite Malaysia being a firmly-established presence on the calendar, the session amounted to a leap into the unknown for the teams after substantial alterations to the Sepang circuit.
"The tarmac has been completely renewed, including alterations to kerbs, drainage and the camber of some corners, we're therefore approach this weekend as if it were a brand new circuit," reported Mercedes technical chief Paddy Lowe.
Ferrari's Kimi Raikkonen was third quickest, just ahead of team-mate Sebastian Vettel, but a second adrift of Rosberg.
Still searching for their first win of the season, Ferrari are running a new floor on both of their cars and are expected to trial a fresh rear wing later in the weekend.
Fernando Alonso was fifth for McLaren in another improved showing from the recovering superpowers. But the Spaniard will be forced to start Sunday's race from the back oft he grid after fitting an upgraded Honda engine. Team-mate Jenson Button, who will use an older power unit, was 10th behind Red Bull pair Daniel Ricciardo and Max Verstappen, and Force India duo Nico Hulkenberg and Sergio Perez.
Malaysia GP Practice One timesheet
1. Nico Rosberg, Mercedes, 1:35.227 (soft tyres)
2. Lewis Hamilton, Mercedes, + 0.494 (medium tyres)
3. Kimi Raikkonen, Ferrari, + 1.088 (soft tyres)
4. Sebastian Vettel, Ferrari, + 1.104 (soft tyres)
5. Fernando Alonso, McLaren, + 1.283 (soft tyres)
6. Daniel Ricciardo, Red Bull, + 1.526 (hard tyres)
7. Max Verstappen, Red Bull, + 1.746 (medium tyres)
8. Nico Hulkenberg, Force India, + 2.286 (hard tyres)
9. Sergio Perez, Force India, + 2.374 (medium tyres)
10. Jenson Button, McLaren, + 2.386 (medium tyres)
11. Daniil Kvyat, Toro Rosso, + 2.620 (soft tyres)
12. Valtteri Bottas, Williams, + 2.634 (medium tyres)
13. Romain Grosjean, Haas, + 2.659 (medium tyres)
14. Esteban Gutierrez, Haas, + 2.694 (medium tyres)
15. Carlos Sainz, Toro Rosso, + 2.828 (medium tyres)
16. Felipe Nasr, Sauber, + 2.957 (soft tyres)
17. Marcus Ericsson, Sauber, + 3.086 (medium tyres)
18. Felipe Massa, Williams, + 3.112 (medium tyres)
19. Jolyon Palmer, Renault, + 3.921 (medium tyres)
20. Esteban Ocon, Manor, + 4.809 (medium tyres)
21. Pascal Wehrlein, Manor, + 5.400 (medium tyres)
22. Kevin Magnussen, Renault, no time set