Mercedes have been looking competitive over a single lap at Sepang for the entire weekend so far. AFP
Mercedes driver Nico Rosberg outshone his more celebrated rivals as he set the quickest pace of the week in final free practice for the Malaysian Grand Prix on Saturday.
The 26-year-old German, still seeking his debut win, blitzed to 1min 36.877sec late in the hour-long session at Sepang, nearly half-a-second up on reigning world champion Sebastian Vettel of Red Bull.
Vettel's team-mate Mark Webber timed third ahead of 2007 world champion Kimi Raikkonen, who was wearing smoke-damaged race gear after a fire gutted the Lotus suite and destroyed his spare helmet.
Finland's Raikkonen, back in Formula One after two years as a rally driver, was already at a disadvantage this weekend after he was penalised five grid places for a change of gearbox.
Stablemate Romain Grosjean was fifth ahead of McLaren's Jenson Button, who won last week's season-opener in Australia, Williams driver Pastor Maldonado, Michael Schumacher and Lewis Hamilton, whose 1:38.021 led Friday's timings.
In relatively cool, overcast conditions, Fernando Alonso was the quicker of the two Ferraris in 13th while his team-mate Felipe Massa, forced on to the defensive over suggestions he could be axed this year, was 18th.
Weather forecasts showed a strong danger of heavy rain around the time of qualifying for Sunday's race, which starts at 4pm (0800 GMT).