Having set the pace during testing at Jerez last week, Sebastien Buemi maintained his position at the head of the times as another three-day test kicked off at the Spanish circuit.
Switching from Toro Rosso over to Red Bull Racing, Buemi posted the quickest lap of the day by some margin, with a quickest time of 1min 17.704secs putting him well clear of second placed Nick Heidfeld.
Buemi focused on data measurement and evaluation of 2009 brakes and was able to work through his complete programme despite going off at turn nine.
Second-placed Heidfeld also hit some problems during the day at the wheel of an interim car based on the 2008 BMW Sauber chassis and fitted with some of the 2009 bodywork. The German worked on set-up options and some tyre testing but he was forced to stop on track with a mechanical issue that led to a precautionary engine change.
Brendon Hartley slotted into third place in the second Red Bull on track as the young New Zealander made his testing debut, while Christian Klien was fourth in the second BMW as he tried out a range of different configurations of the KERS system.
Williams test driver Nico Hulkenberg completed the five drivers on track with the fifth quickest time.
For testing times, CLICK HERE