Antonio Pizzonia produced an impressive display in testing to boost his bid for a drive at Williams next season.
Antonio Pizzonia stood in for Ralf Schumacher last season
The Brazilian has emerged as favourite to partner Mark Webber after temporarily stepping in to replace the injured Ralf Schumacher this year.
He ended with the second fastest time of the day in Barcelona, just behind Ricardo Zonta but almost half-a-second quicker than Webber.
Sauber's Jacques Villeneuve was third while Pedro de la Rosa ended in fourth.
McLaren team-mate Juan Pablo Montoya set the fifth fastest time while BAR's Jenson Button could only finish in 13th.