Sepang: Mercedes confirmed it is the team to beat at the Formula One Malaysian Grand Prix by setting the fastest times in both of Friday's practice sessions, although its rivals are closer than expected.
Nico Rosberg, coming off his win at the season-opening race in Australia, was fastest in the second session and overall with a time of 1 minute, 39.909 seconds around the Sepang International Circuit, bettering Ferrari's Kimi Raikkonen by just three hundredths of a second.
Raikkonen, who struggled in Melbourne, was also second fastest in the morning session behind's Rosberg's Mercedes teammate Lewis Hamilton.
Although Mercedes was expected to dominate the early races of the season, and did so in Australia, the top six cars in Friday's afternoon session were separated by just two-tenths of a second, indicating a competitive race on Sunday.
Defending four-time world champion Sebastian Vettel overcame some technical issues that restricted his running in the morning session and was an impressive third fastest in the afternoon, while his Red Bull teammate Daniel Ricciardo was seventh.
The bad news for Vettel was that he needed to change his power supply unit - which distributes the power supply between the engine, the turbo and the battery-stored energy. That means he is onto his third of the season, with a limit of five all year before penalties kick in.
Hamilton was fourth in the second session, ahead of Ferrari's Fernando Alonso and Williams' Felipe Massa. Hamilton is using the same engine that caused his early retirement from the Australian race, with the team having fixed the misfire.
McLaren's Jenson Button was eighth quickest, bettering Williams driver Valtteri Bottas and Force India's Nico Hulkenberg.
On a typically hot but dry day at Sepang, all drivers suffered with technical issues of some kind, ranging from the lack of downforce on the new cars which caused several off-track excursions, high tire-wear from the consequent sliding and fuel consumption issues with the new V6 turbo hybrid engines and the introduction of fuel usage limits.
Lotus and Caterham were, as in Melbourne, the teams to suffer most.
Neither Lotus car completed a lap in the morning as the team continued to play catch-up on its engine development after a strife-torn offseason. Pastor Maldonado sat out the afternoon too, and while Romain Grosjean made several trips out on track, he suffered repeated breakdowns.
Caterham's Kamui Kobayashi suffered yet more problems with his energy-storage system, necessitating another replacement after two in Melbourne, meaning he is already closing in on the season limit of five despite only being at the second meeting of a 19-race season.