Vettel, who considers himself to be the outsider in the five-way championship battle, ran with an upgraded aero package, including a new rear wing, and clocked a time of 1:46.660 around the floodlit Marina Bay Street Circuit – more than half a second ahead of Webber, and more than a second ahead of the rest.
Conditions in the second practice were similar to those expected for SundayÃ¢â‚¬â„¢s race with times set far quicker than those clocked on the damp track in the earlier session, with the front runners expected to be encouraged by their running.
Vettel told reporters: Ã¢â‚¬Å“The most important thing is to have a clean Friday and we had no problem with the car today.
Ã¢â‚¬Å“It doesn’t mean so much to be fastest today as it’s only practice and there are no points available but it’s still good to be on top and we have good pace.Ã¢â‚¬Â
McLarenÃ¢â‚¬â„¢s cars are expected to run well this weekend and world champion Jenson Button improved from FP3 to finish just behind Webber, with team-mate Lewis Hamilton fifth on the timesheets, behind championship rival Fernando Alonso.
The SpaniardÃ¢â‚¬â„¢s Ferrari continues to impress late in the season despite a rumour of engine problems for the Italian team.
The top five drivers in the championship are separated by just 24 points and with five races remaining, the slightest mistake in qualifying or the race could spell the end of a number of bids.
Alonso was unable to restart his car after skidding into a runoff area while trying to challenge VettelÃ¢â‚¬â„¢s fastest time.
Ã¢â‚¬Å“This morning we wanted to do more mileage but the conditions could not make that possible,Ã¢â‚¬Â said Ferrari team principal Stefano Domenicali.
Ã¢â‚¬Å“The situation improved in the afternoon but it’s difficult to judge where we are after Fernando had a slight problem when he was running quickly.
Ã¢â‚¬Å“It’s tough to know how fast we are compared to the others but we will try our best in qualifying.Ã¢â‚¬Â
Rubens Barrichello continued Williams recent good run of form, taking an encouraging sixth for the team ahead of Felipe Massa in the second Ferrari.
FridayÃ¢â‚¬â„¢s first action in Singapore took place on a drying track after a mid-afternoon downpour with the majority of the teams waiting for conditions to improve before making reasonable runs.
Webber set the quickest time in 1:54.589 to edge out Mercedes GPÃ¢â‚¬â„¢s Michael Schumacher by 0.119 seconds as the seven-time world champion led a trio of Germans around the street circuit, recording his best result in free practice.
Force IndiaÃ¢â‚¬â„¢s Adrian Sutil was third fastest in 1:54.827 while Vettel completed just 12 laps to take fourth place with a 1:55.137.
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