Ferrari's Kimi Raikkonen set a blistering pace on the second day of testing at the Sepang circuit, where 10 of the 11 Formula One teams are working this week.
The Finn driver, winner of the season-opening Australian Grand Prix, posted a best time of 1:35.268 to edge his nearest rival by nearly half a second after 61 laps.
Raikkonen's time was almost a whole second quicker than yesterday's best, set by BMW Sauber's Robert Kubica.
The day was again sunny and hot, with air temperatures of 34 degrees Celsius and track temperatures reaching 54.
Raikkonen, the only Ferrari driver on track, outpaced Williams' Alexander Wurz, who enjoyed another promising session with the Toyota-powered FW29. The Austrian managed a total of 114 laps, the most by any driver today.
Scot David Coulthard also had a strong day for Red Bull Racing, setting the third fastest time as the team continue to work on making progress with their RB3.
Ralf Schumacher, taking over from Toyota's third driver Franck Montagny, finished in fourth, the German continuing with set-up comparison work ahead of the Malaysian Grand Prix next week.
Schumacher caused one of the three red flags of the day when he spun around 15:20.
"It was a reasonable day," Schumacher told autosport.com. "There were no mechanical problems, which was positive. Basically we prepared for the race, we tried both tyres and we have some interesting data to chase tonight."
Kubica showed BMW Sauber are making progress with their reliability after covering nearly two Grand Prix distances with the F1.07. The Pole was fifth quickest, ahead of McLaren's Lewis Hamilton, who joined the test today replacing test driver Pedro de la Rosa.
Hamilton's day finished two minutes early when he stopped on track just as the session was about to end.
The Super Aguri team had their two drivers in action, with Anthony Davidson returning to work after injuring his back at the Australian Grand Prix.
With testing rules allowing teams to run with just one car, Davidson shared his car with teammate Takuma Sato, who drove in the morning.
Super Aguri were used by Bridgestone to test a new tyre marking, after the red dot tested yesterday did not prove successful.
Brazilian Rubens Barrichello, eighth quickest for Honda, caused the other red flag of the day when his engine blew up just half an hour into the session. He still managed to finish ahead of teammate Jenson Button, who drove in the afternoon but covered just 24 laps.
The Honda drivers were split by Renault's Heikki Kovalainen, ninth fastest after a good day of work.
"This was a pretty positive first day for me," said the Finn. "It is great fun driving here. The conditions are incredibly hot, but the track was really enjoyable to drive. I felt comfortable straight away, was able to push hard and the times were consistent.
"The balance of the car was pretty good, and we did some interesting tests. We learned a lot today, and we will try and build on that tomorrow."
Toro Rosso were the third team with two drivers on track, Tonio Liuzzi joining Scott Speed for the day.
Pos Driver Team Time Laps 1. Raikkonen Ferrari (B) 1:35.268 61 2. Wurz Williams-Toyota (B) 1:35.702 114 3. Coulthard Red Bull-Renault (B) 1:35.712 87 4. R.Schumacher Toyota (B) 1:35.751 81 5. Kubica BMW-Sauber (B) 1:35.887 111 6. Hamilton McLaren-Mercedes (B) 1:36.115 69 7. Sato Super Aguri-Honda (B) 1:36.306 63 8. Barrichello Honda (B) 1:36.563 36 9. Kovalainen Renault (B) 1:36.578 86 10. Button Honda (B) 1:36.617 24 11. Davidson Super Aguri-Honda (B) 1:37.876 39 12. Speed Toro Rosso-Ferrari (B) 1:37.910 36 13. Liuzzi Toro Rosso-Ferrari (B) 1:37.971 32 All Timing Unofficial