Buemi quickest at wet Portimao

The weather conditions, however, were less than favourable for the five teams on track, and the Portuguese circuit was damp or wet throughout the whole session.

A downpour near the end of the day caused little action to happen in the last two hours.

Toro Rosso driver Buemi was the only man at the wheel of a 2008-spec car, with the other four teams running with new machinery.

The Swiss finished nearly five seconds ahead of Pedro de la Rosa, who completed the first proper run with the new McLaren MP4-24 unveiled on Friday.

The Spanish driver's car was fitted with a 2008 rear wing, that offered more stability in wet conditions to do various electronic checks.

De la Rosa finished less than three tenths of a second ahead of Nico Hulkenberg in the new Williams FW31, unveiled today.

Despite the poor weather, Williams were pleased with the initial roll-out.

"This morning has been full wet, but the weather hasn't really affected what we wanted to do, because our goal has been to get the car out on track, check all the systems work, be sure parts aren't touching each other, nothing is burning, and that's all proved to be okay," said technical director Sam Michael.

"It would be good to get some dry running, and the weather should allow this later in the week. In terms of first impressions of the car, we of course haven't spent any time on set-up or performance work yet, that'll all come later, but so far the car is running fine."

Nelson Piquet was the man in charge of rolling out the new Renault R29, the Brazilian completing 33 laps.

"It feels great to be in the R29, even though the weather was not great," said Piquet. "Today was all about adding miles to the car, collecting data and learning as much as we could. Hopefully the rest of the week will allow us to build on the progress we have made today."

Toyota's Kamui Kobayashi, whose team were in action at Portimao yesterday, finished at the bottom of the times at the wheel of the TF109 launched last week.

"Today has gone well and I am happy with the new car," said the Japanese driver. "It has been an interesting experience to drive with KERS for the first time and we are understanding more about the system all the time.

"This is my first time driving at this track and I have to say I am very impressed; the lay-out is really exciting and quite challenging for a driver. The weather was far from ideal, especially in the afternoon, so that meant we could not spend as much time on track as we planned."

Today's times:

Pos  Driver        Team                       Time     Laps
 1.  Buemi         Toro Rosso-Ferrari   (B)  1:41.528   65
 2.  de la Rosa    McLaren-Mercedes     (B)  1:46.076   28
 3.  Hulkenberg    Williams-Toyota      (B)  1:46.335   28
 4.  Piquet        Renault              (B)  1:48.907   33
 5.  Kobayashi     Toyota               (B)  1:50.989   46

All Timing Unofficial