Highlights - Webber sets first practice pace
Mark Webber was fastest in first practice for the Singapore Grand Prix after a session rendered largely academic by damp track conditions.
Rainstorms during the day had left standing water in places, and high humidity slowed the drying process.
Only in the final few minutes did the title contenders begin to test their cars on slick, dry-weather tyres.
Michael Schumacher was second fastest for Mercedes, with Adrian Sutil's Force India third quickest.
The skies were clear but the track was decidedly wet, with puddles in some areas, when the drivers came out for their installation laps at the start of practice, 1800 Singapore time.
To add to their difficulties, resurfacing work rendered much of the data from previous races redundant.
Unsurprisingly most chose to feel their way around on intermediate tyres, with Christian Klien, standing in for the indisposed Sakon Yamomoto at Hispania, the first to set a time at two minutes 18.621 - more than 20 seconds slower than Webber's final lap.
Given the qualifying pace last year was around 1.46 it was not going to be long before improving conditions saw the times begin to fall.
Half an hour into the session, Timo Glock's Virgin was round in 2.03.286, and as darkness began to fall, Sauber's Kamui Kobayashi dipped under two minutes, but after an hour it was apparent the title-contenders were going to wait until slick tyres could be fitted before showing their hands.
Having initially sent out Felipe Massa on worn intermediates, Ferrari finally switched the Brazilian to slicks. Fernando Alonso cruised around behind him, collecting data before immediately switching to a different front wing.
Schumacher was second fastest on the Marina Bay circuit
With just 16 minutes remaining Jenson Button's McLaren nosed out of the pitlane for a four lap run on slicks, with Red Bull's Sebastian Vettel and Button's team-mate Lewis Hamilton following.
Championship leader Webber was the last of the main men to emerge, and with traffic always likely to be a factor, it looked as though Schumacher might top the practice charts for the first time in a tough season for the former world champion.
As it was Webber denied the German a reminder of times past. If conditions continue to dry, the normal order is likely to be restored during second practice.
Webber's time of 1.54.589 nosed out Schumacher by 0.119 seconds. Vettel was fourth fastest, with Button sixth. Alonso was 11th fastest, Hamilton - who only completed nine laps - was 18th, one place ahead of Massa.
Webber focused on 'special challenge'