Mercedes' Lewis Hamilton failed to set a time in the Malaysia Grand Prix's opening practice session on Friday, while Fernando Alonso struggled with his brakes on his return to Formula One.
On his first time out on the track at Sepang International Circuit, Hamilton only made it to turn eight before being told to park, after he had reported a "click" in the back of his car.
Mercedes were not receiving telemetry in pit lane, so they told him to stop rather than risk a race engine.
Mercedes later confirmed that it was an engine problem and the reigning champion was forced to sit out the rest of the morning session in Malaysia.
It was not all bad news for Mercedes, however, with Nico Rosberg (1:40.124) setting the fastest time, while Ferrari followed up Sebastian Vettel's third-place finish at the Australian Grand Prix on March 15 with decent pace.
Vettel (1:40.985) and team-mate Kimi Raikkonen (1:40.497) were Rosberg's closest rivals throughout the session.
Alonso made his first appearance of the 2015 campaign after missing the entire week in Melbourne following his pre-season crash in Barcelona, but the Spaniard languished with a best time of 1:42.885 after locking up his brakes while cornering a number of times.
Williams' Valtteri Bottas also returned from injury and managed 1:41.882 to finish eighth.
FP1 classification:
1.Nico Rosberg (Mercedes) 1:40.124
2.Kimi Raikkonen (Ferrari) 1:40.497
3.Sebastian Vettel (Ferrari) 1:40.985
4.Romain Grosjean (Lotus) 1:41.543
5.Carlos Sainz (Toro Rosso) 1:41.596
6.Daniel Ricciardo (Red Bull) 1:41.787
7.Max Verstappen (Toro Rosso) 1:41.803
8.Valtteri Bottas (Williams) 1:41.882
9.Daniil Kvyat (Red Bull) 1:42.055
10.Marcus Ericsson (Sauber) 1:42.064