Michael Schumacher in the pits in Imola on Friday. (Reuters)

Imola: Briton Jenson Button fired a warning shot to BAR?s rivals in San Marino Grand Prix practice on Friday.

While McLaren?s Spanish test driver Pedro de la Rosa set the fastest time, Button was the quickest of those who will race in Imola on Sunday and comfortably ahead of Ferrari in the struggling champions? backyard.

Ferrari?s Michael Schumacher was sixth fastest in the afternoon, 1.541 seconds slower than De la Rosa?s lap of one minute 20.484 with teammate Rubens Barrichello seventh.

Honda-powered BAR and Button have yet to finish in three races but the Briton took his first pole position in Imola last year and finished second behind Schumacher, who has made his worst start to a season. BAR completed some 6,000km in five days of testing last week and are confident they have resolved their early season problems.

Schumacher has won five times in the last six years in Imola and needs a strong result with the new F2005 after a hydraulics problem sidelined him on the car?s hurried debut in Bahrain three weeks ago.

The German is 24 points behind young Spaniard Fernando Alonso, Renault?s championship leader who has won the last two races from pole position.

Friday?s times, admittedly a poor guide to race form, offered Ferrari?s home fans little prospect of a quick return to the team?s 2004 dominance when they won 15 of 18 races.

Alonso was fifth fastest in the afternoon after holding fire in the first hour-long morning session, when neither he nor Italian team mate Giancarlo Fisichella set a time. Fisichella was ninth in the second stint.

De la Rosa, who competed as a stand-in for injured Colombian Juan Pablo Montoya in Bahrain, has handed over the race seat to Austrian Alex Wurz who was eighth quickest on Friday afternoon.

Toyota?s Brazilian test driver Ricardo Zonta was second quickest in the morning. Italian Jarno Trulli, who has brought Toyota two second place finishes in the last two races, did not set a timed lap in the first session and was 13th in the second.

Narain Karthikeyan finished at 16th spot in the first session and was 17th in the second.

Race drivers limit their practice mileage on Fridays because of new regulations forcing them to use the same engines for two successive GPs. (Reuters)