Singapore: Championship-chasing German Sebastian Vettel topped the times in Friday`s second free practice session ahead of this weekend`s potentially-decisive Singapore Grand Prix.
The 24-year-old Red Bull driver clocked the fastest lap of one minute and 46.374 to finish the day two-tenths of a second ahead of nearest rival two-time champion Spaniard Fernando Alonso of Ferrari.
Briton Lewis Hamilton of McLaren, quickest in a incident-packed opening session, came third in the later run ahead of Brazilian Felipe Massa in the second Ferrari.
The first practice was delayed because of problems with kerbing along the Singapore street-circuit and when proceedings finally began 30 minutes late it was punctuated by red flagged interruptions for various minor incidents.
The second period of action was more straightforward as the teams acclimatised to the choking heat of 32 degrees Celsius and heavy humidity, with the main talking point being Jenson Button`s mid-practice withdrawl.
His participation in the session ended after he almost lost control of his McLaren under braking at Turn 14.
A pair of lurid skid-marks on the circuit suggested he had locked up as he battled to keep the car under his guidance. When he had stopped, his team suggested he tried to reverse the car and return to the track.
Button replied, abruptly, that his reverse gear was "not working" before climbing out and taking a scooter ride back to the pits.
Better luck followed Australian Mark Webber, who was fifth in the second Red Bull ahead of seven-times champion German Michael Schumacher, 42, of Mercedes, who was two seconds off the pace set by his compatriot Vettel.
Another German Adrian Sutil of Force India was seventh ahead of Mexican Sergio Perez and his Sauber team-mate Japanese kamui Kobayashi. Button clocked in tenth.