Brazilian veteran Rubens Barrichello topped the times for Brawn GP after the opening free practice session for this weekend's European Grand Prix.
The 37-year-old Barrichello clocked a best time of one minute and 42.460 seconds around the Mediterranean harbour street circuit with 15 minutes remaining on a hot morning in eastern Spain.
Finn Heikki Kovalainen was second fastest for McLaren ahead of his team-mate, defending drivers world champion Lewis Hamilton of Britain, who won his first race of the season at last month's Hungarian Grand Prix.
Championship-leading Briton Jenson Button was fourth in the second Brawn at the conclusion of an eventful morning's action which ended with Barrichello's car struggling with gearbox problems as he went for an even faster lap time.
Button was fastest for a long period during the morning, but ended up six-tenths of a second off Barrichello's pace, but the duo's overall performance suggested that Brawn have rediscovered some of their best form after three races in the doldrums.
German Sebastian Vettel was the top Red Bull driver in fifth position ahead of compatriot Adrian Sutil, who was sixth for the much-improved Force India team.
Japanese Kaazuki Nakajima was seventh for Williams ahead of Australian Mark Webber in the second Red Bull with two-times champion Spaniard Fernando Alonso of Renault and Finn Kimi Raikkonen of Ferrari completing the top ten.
The session saw a flurry of incidents, but no serious accidents, as many drivers ran wide over the kerbs on the dusty asphalt circuit.
French debutant Romain Grosjean of Renault was 17th, more than a second slower than team-mate Alonso and veteran comeback driver Italian Luca Badoer, replacing injured Brazilian Felipe Massa for Ferrari, was 20th, two seconds down on Raikkonen.