Red Bull driver Mark Webber set the fastest time in Friday's practice sessions for the Formula One Malaysian Grand Prix, edging out McLaren's Jenson Button. (In pics)
Webber was just five hundredths of a second quicker than Button, with McLaren's Lewis Hamilton and Red Bull's Sebastian Vettel both within a quarter of a second - setting the stage for a qualifying clash between the top two teams on Saturday.
There was a gap between those drivers and the rest of the field on a humid but dry day at the Sepang circuit. Mercedes drivers Michael Schumacher and Nico Rosberg were fifth and seventh respectively, and Ferrari's Felipe Massa was in sixth.
Webber's performance will be a boost for him personally after a disappointing season opener in his home Australian Grand Prix, but more importantly for the team, it shows that the drivers can perform strongly while using the KERS power boost system. The team didn't use the device in Melbourne's qualifying and race.
Renault had a troublesome day, losing plenty of running time after both of its cars suffered wheel and suspension failures in the morning practice run. In the most worrying incident, the upright part of the suspension on Vitaly Petrov's car collapsed under braking, sending the Russian spearing across a gravel trap.
Both Renault drivers were sent out midway through afternoon practice, with Nick Heidfeld setting the eighth-fastest time of the session, bettering Ferrari's Fernando Alonso in ninth and Toro Rosso's Jaime Alguersuari in tenth.
Williams' rookie Pastor Maldonado had the 11th-best time in the session after he ran onto the grass while trying to enter the pit approach road and spun into a fence.
Hispania also had a tough day, with both of its cars suffering mechanical failures and Narain Karthikeyan facing punishment after speeding in the pitlane.
However, both Hispania drivers looked capable of qualifying for Sunday's race after finishing within 7 percent of Webber's time in the afternoon session. Drivers need to be within 7 percent of the best car in the first part of Saturday's qualifying or they can't race. Both Hispania cars did not make it under the threshold in Australia.
Virgin's Jerome d'Ambrosio did not participate in the afternoon practice after his car experienced a suspension problem in the morning session that his team was unable to resolve.
Having not had the chance to test their wet weather tires Friday, teams will be hoping the tropical rain holds off for Saturday's qualifying and Sunday's race, though forecasts indicated a high probability of a downpour on Sunday.