BARCELONA: Formula One leader Jenson Button of Brawn GP was fastest in the first practice session for the Spanish Grand Prix on Friday.

Button set a fastest lap time of 1 minute, 21.799 seconds at the Circuit de Catalunya as several car upgrades helped maintain the British driver's pace and kept him as favourite to win Sunday's race.

Button has won three of the first four GPs to lead teammate Rubens Barrichello by 12 points in the drivers' championship.

Toyota's Jarno Trulli was second with a best lap of 1:22.154, while BMW Sauber turned in much-improved performances as Robert Kubica and Nick Heidfeld came next.

BMW Sauber was coming off a terrible showing at Bahrain where its drivers finished 18th and 19th. The German team will need a strong performance here to maintain its championship hopes.

Kazuki Nakajima of Williams was fifth with a best lap of 1:22.659 to lead teammate Nico Rosberg.

Ferrari showed better pace on the back of aerodynamic upgrades, with Felipe Massa finishing ninth - 0.855 off Button's time - while Kimi Raikkonen was 11th. Raikkonen's last victory came here last year.

Barrichello was 10th while Red Bull's Sebastian Vettel, who trails Button by 13 points to sit third in the overall standings, placed 13th.

Defending champion Lewis Hamilton was 14th, 1.278 seconds behind Button, as F1 begins its European run of nine races.