SEPANG, Malaysia (AP) -- Mercedes confirmed it was the team to beat at the Malaysian Grand Prix by setting the fastest times in both of Friday's practice sessions, although its Formula One rivals were 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, exceeding Ferrari's Kimi Raikkonen by three-hundredths of a second.
Raikkonen, who struggled in Melbourne, was also second fastest in the morning session behind 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 on Friday afternoon were separated by just two-tenths of a second, indicating a competitive race on Sunday.
''We are still having some small issues and therefore we were not able to maximize everything today,'' Rosberg said. "The quickest teams seem to be closer together than in Australia, so we still have work to do overnight to improve our level of performance.''
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 computer power supply unit, which alternates the power source between the engine, the turbo and battery-stored energy. That means he is onto his third of the season, with a limit of five all year before penalties kick in.
''Friday timings are not the most important in the world, but to be out there in the range with the other guys was a decent day,'' Vettel said.
''It was not a completely smooth day for both of us; for myself, still some things to solve on the software side, programming the car, which sounds wrong but that is the way it is.''
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 GP, with the team having fixed the misfire and preserved an engine which is also subject to the same five-per-season limit.
McLaren's Jenson Button was eighth quickest, ahead of Williams driver Valtteri Bottas and Force India's Nico Hulkenberg.
On a typically hot but dry day at Sepang, all drivers endured technical issues of some kind, ranging from the lack of downforce 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.
As in Melbourne, Lotus and Caterham were the teams to suffer most.
Neither Lotus car completed a lap in the morning as the team continued to play catchup 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 had 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.