World champion Michael Schumacher [ Images ] kept Ferrari [ Images ] in a class of their own in Friday's first practice for the San Marino Grand Prix [ Images ].

The German was a hefty 1.359 seconds quicker than his Brazilian team mate Rubens Barrichello [ Images ] and 2.166 faster than his younger brother Ralf in a Williams.

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The time was surprising only by the enormous gulf between the red cars and the rest, with Schumacher heavily favoured to chalk up his fourth win in four races this season.

The six-times world champion has won the San Marino Grand Prix, Ferrari's home race at a circuit named after late founder Enzo and son Dino, four times in the past five years and is also chasing his fourth successive pole position.

Briton Anthony Davidson [ Images ], the BAR test driver, was fourth quickest ahead of team mate Jenson Button [ Images ] who has finished the last two races on the podium.

McLaren [ Images ] again looked to be struggling, with Finland's Kimi Raikkonen [ Images ] eighth fastest and Briton David Coulthard [ Images ] 11th. Raikkonen, last season's championship runner-up, has yet to finish a race this year.

Sunday's race marks the 10th anniversary of the death of Brazilian champion Ayrton Senna at the circuit and could also be Imola's final appearance on the Formula One calendar.