Sepang, Malaysia (Reuters) - Nico Rosberg dominated the first free practice session for the Malaysian Grand Prix on Friday but Mercedes were left scratching their heads after team mate Lewis Hamilton suffered a major engine problem.
Rosberg clocked a fastest lap of one minute, 40.124 sec around the sweeping 5.54 km Sepang International Circuit to finish ahead of the resurgent Ferraris of Kimi Raikkonen and Sebastian Vettel on a sweltering morning in Malaysia.
Fernando Alonso enjoyed a smooth return to action after missing the season-opening race in Australia due to concussion caused by a crash in winter testing, the Spaniard completing 20 laps in his McLaren to finish 14th after 90 minutes of action.
The session was also notable for Manor Marussia, who despite setting the slowest times of the morning, were able to get their modified 2014 cars out on the track after failing to even manage that in Melbourne.
Up at the business end of the field it was a bittersweet session for Mercedes, who would have been happy to see Rosberg finish 0.373 sec clear of Raikkonen but disappointed that world champion Hamilton's stint ended prematurely.
The Briton ground to a halt at the problematic Turn Nine hairpin after starting the session without telemetry, Hamilton complaining of an issue at the rear of the car as he stopped without setting a timed lap.
"There was a click in the rear. The gears still worked, but I pulled over and stopped as you told me to. I would have made it back," Hamilton, who led a Mercedes one-two in the season-opening race, told his team over the radio. "We haven't got any telemetry mate so we're just a bit worried about this as it's a race engine. We don't want to risk it any more," Hamilton's race engineer Peter Bonnington said in response.
The stricken Mercedes was eventually returned to the garage on a flat-bed truck and quickly stripped down by mechanics, who set about repairing Hamilton's engine ahead of the second session.
With only four power units available for the 19-race season, Mercedes will be hoping to recover the initial engine to compete in at least three or four more grands prix or the team could be on course to face a penalty for surpassing their annual quota.
"There is a hardware problem that we need to go and fix, so we don't know exactly what we are going to do yet. We need to do some investigations in the next few minutes to decide what we are going to do for P2," technical director Paddy Lowe said in a trackside interview.
Of the other teams, Williams will be disappointed with their session as Valterri Bottas, also returning from injury, could only manage the eighth fastest time with team mate Felipe Massa down in 11th.
Daniel Ricciardo got his underperforming Red Bull up into sixth place, although the Australian did complain of "weak traction" to his team over the radio early on.