(CNN) -- Nico Rosberg kept up Mercedes impressive start to the 2014 Formula One season by posting the fastest time of a tight practice day at the Malaysian Grand Prix.
The German driver edged out Kimi Raikkonen of Ferrari and Sebastian Vettel of Red Bull with a time of one minute and 39.909 seconds in the afternoon session -- but it was close. Just 0.061 seconds separated the three drivers.
Rosberg's Mercedes team-mate Lewis Hamilton, who clocked the fastest time on the morning timesheet, ended the day fourth closely followed by Ferrari's Fernando Alonso and Williams' Felipe Massa.
Temperatures reached a mercury-busting 50 degrees at the Sepang Circuit, impacting tire performance in the afternoon session.
"It was crazy conditions out there," Rosberg, who took the checkered flag at the season opening Australian Grand Prix earlier this month, told the sport's official website. "In the very, very warm temperatures, it's a huge challenge to get everything right."
"The tires are behaving very differently from how they did in Australia -- so that'll be my focus. Still, I'm convinced we can make some useful changes to the car overnight."
Rosberg's concerns surrounding the sweltering conditions were echoed by his teammate and 2008 world champion Hamilton.
"It was pretty tough with the temperature and humidity and it's so important to keep hydrated here," said the Briton, who was forced to retire from the season's opening race.
"The car feels good and our focus was on trying to understand the tires and make sure the balance is right for the weekend," he added.
Red Bull rising?
Another man pleased with how the sessions went was Red Bull's Sebastian Vettel. The reigning F1 champion and dominant driver pulled out of the Australian Grand Prix after just six laps.
He also suffered the indignity of failing to reach the third qualifying stage for the first time since 2012.
"I think we had a good day, obviously Friday timings are not the most important thing in the world but it's good to be up there and in range of the top guys," said Vettel.
"There are still some things to solve on the software side and the programming, but that's the way it is. I think we have to learn a lot but all in all, I'm quite happy."
Vettel's Red Bull teammate Danny Ricciardo finished the day seventh fastest, just ahead of Jenson Button of McLaren and Valterri Bottas of Williams.
Elsewhere, McLaren rookie Kevin Magnusson failed to capture the speed which saw him finish second at Victoria Park. The Dane ended the day 12th fastest and highlighted the extreme heat as major factor in how his car performed.
"I've never driven a car in these sorts of temperatures, so I learned a lot today, Magnusson said. "The track temperatures are so hot here that the tyres are really suffering, but it's the same for everyone.
"We need to try and get on top of things before tomorrow's sessions."
Flight MH370 tribute
Before the race at the Sepang Circuit on Sunday teams, drivers and officials are planning a host of tributes to passengers of missing flight MH370.
The race track neighbors Kuala Lumpur's main airport where the plane took off on March 8.
Lewis Hamilton showed his support for the gesture yesterday, tweeting a picture of his car bearing the hashtag "#PrayForMH370" along with the message: "All my prayers and sympathies go to the friends and families of the passengers on MH370 flight."