Australian Grand Prix, dodged a heavy shower to clock the day's fastest time of 1min 36.569sec in the second session.
Kimi Raikkonen finished at the top of a practice session for the first time since his comeback to Formula 1 last year. Getty Images
Red Bull's Sebastian Vettel, on the hunt for his fourth straight world title, was just two-hundredths of a second slower at the tropical Sepang circuit while Felipe Massa and Fernando Alonso were third and fourth for Ferrari. Red Bull pilot Mark Webber, who led the opening 90-minute session, timed fifth in the second stanza while Lotus's
Romain Grosjean was sixth, despite a bumpy excursion across the trackside grass.
Nico Rosberg, Paul di Resta, Lewis Hamilton and Adrian Sutil were the remaining top 10 drivers after a difficult session which was punctuated by a track-clearing deluge midway through.
Tropical heat and sudden downpours make the Malaysian Grand Prix one of the most demanding of the season, with an extra challenge this year in preserving Formula One supplier Pirelli's new, faster-degrading tyres.
Raikkonen is a two-time winner at Sepang, including his first ever Formula One victory in 2003. But the Finn said Friday's performance would matter little when it comes to qualifying on Saturday.
"It seemed to be OK today... it was a good day but it doesn't help us tomorrow so we have to do tomorrow and hope it goes well," he said, dismissing the challenging conditions as "the same like other years".
Lotus technical chief James Allison said the 33-year-old Raikkonen, embarking on his second season in Formula One after his return from a two-year stint in rallying, seemed in a good frame of mind and had shown it with the win in Australia.
"He's certainly very, very relaxed and confident this year and he drove the race incredibly patiently," Allison said.
"I think he knew he had a good car under him, he knew he didn't have to scamper up behind the group in front and he looked after the tyres, only going quickly when he needed to. It was just a very mature, and smooth and fast race."
Vettel said Friday's stop-start afternoon session had yielded few results but the earlier run-out had shown the tyres will not last long on the hot, abrasive circuit.
"This afternoon we couldn't do so much due to the weather, but this morning it looked okay, although the tyres don't last very long," Vettel said. "We need to try a couple of things now overnight to improve and take a steps forward."
After a disappointing outing at the Australian Grand Prix, there will be further concern in the McLaren camp with newcomer Sergio Perez and 2009 world champion Jenson Button finishing the day in 11th and 12th respectively.