By Patrick Johnston
SEPANG, Malaysia (Reuters) - Mercedes' early season strength was again evident with Briton Lewis Hamilton going fastest in Friday's first practice for the Malaysian Grand Prix in a session where many cars struggled for grip.
The 2008 world champion clocked a best time of one minute 40.691 seconds at the Sepang Circuit on a scorching hot Friday where track temperatures reached 44 Celsius (111 Fahrenheit) during the 90 minute session.
However, Hamilton was one of many drivers who encountered the Malaysian gravel after locking his wheels and the Briton said over the team radio the Sepang track was "like driving on marbles".
Ferrari's Kimi Raikkonen was second quickest in a promising session for the Finn who clocked a best time of 1:40.843 just ahead of Hamilton's team mate Nico Rosberg, who won the season opener in Australia two weeks ago.
Jenson Button was fourth quickest ahead of McLaren team mate Kevin Magnussen, whose car stopped on the track at turn 15 and needed a push from the marshals to get back to the pits with 30 minutes remaining.
The Danish rookie, second in Australia on his F1 debut, was back out on the track later in the session, though, relieving fears of a more serious issue with his car.
However, there was plenty of concern in the Lotus garage with neither Romain Grosjean or Pastor Maldonado able to complete a timed lap as both encountered issues.
The French driver stopped at turn 10 and had to be pushed off the track by marshals early in the session, while smoke billowed out of the back of Maldonado's car in the final minutes and he was told to switch off the engine by a concerned team.
Jean Eric Vergne was sixth for Toro Rosso but his rookie Russian team mate Daniil Kyvat was 14th after telling his team over the radio the car was "undriveable".
World champion Sebastian Vettel was seventh quickest, almost a second behind Hamilton, after managing only nine laps, while team mate Daniel Ricciardo managed to clock 20 laps and finished 12th.
Ferrari's Fernando Alonso was first out of the pits in the session and had set the early pace before ending in 11th as he also suffered problems with grip and spun at turn eight but managed to continue.
The same corner also caught out the Spaniard's former team mate Felipe Massa but the Williams driver also resumed, while Sauber's Adrian Sutil ran wide at turn 15 but kept the car going before making it back on the track.
Friday's second session ahead of Sunday's race starts at 0600 GMT.
(Editing by Greg Stutchbury)