Pit-stop strategy helped Rinaldo Capello and Tom Kristensen take American Le Mans Series victory in the X-Factor Grand Prix of Sonoma.at Sears Point Raceway.

The drivers benefited from a team decision to stretch time between pit-stops in the two-hour 45-minute endurance race, which helped to overcome a stern challenge from Joest team-mates Frank Biela and Emanuele Pirro. The decision allowed this year's unbeaten team to turn its final pit-stop into a 20-second fuel splash that kept the Audi R8 in the race lead.

Championship leader Capello and Kristensen went on to score a 6.674secs win over Pirro and Biela, and the winning Italian was convinced that the strategy was the key in allowing him to take his third ALMS win of the this season.

''Our cars were very even,'' he said of the two Audi factory machines, ''It was only the traffic that separated us on the track, but they made the wrong strategy and you can see the result.''

David Brabham and Jan Magnussen, driving a Panoz LMP-1, finished third, on the lead lap with the two Audis.

The race began, as expected, with the two works Audis pulling away from the rest of the field, a task eased as Brabham moved the lead Panoz ahead of the Champion Racing R8, preventing Andy Wallace from mixing it with the two silver machines. Capello, from the pole, slowly eked out an advantage over Biela, establishing a pattern that would last throughout the race, although the red and yellow-hued cars would enjoy some close quarter dicing as the event wore on.

Wallace remained stuck behind Brabham's well-driven Panoz for what must have seemed an eternity, and led to a change in strategy for the Champion team, as it elected to reverse its pit-stop programme and use the expected late race 'splash-and-dash' to try and find some clear track for the white R8.

The plan went to pot at around the one hour mark, when the first caution flags flew for a clash between two of the GT Porsches. With the leaders now able to pit under yellow, Champion found itself still behind the pesky Panoz, as the two Joest-run Audis continued to make good their escape.

A second full course caution not long after the first - brought about by one of the two Cadillacs attempting to three-wheel back to the pits - also failed to reverse the order of the third-fourth battle, leaving the Champion team champing at the bit in frustration. Now with former GP drivers Jan Magnussen and Johnny Herbert at the wheel of the Panoz and Audi respectively, the two cars battled right to the end, but it was the 2000-spec Roadster that came out on top of the 2000-spec R8.

The rest of the prototype field endured a troubled day, with the second Panoz grinding to a halt with a box full of neutrals as early as lap 19. Emmanuel Collard's Cadillac finished twelfth, some twelve laps down on the leader, while the other car was the last classified finisher, despite completing only just over half the distance of Capello's Audi after the wheel problem. The Intersport Lola, forced to start at the back after opting to change tyres between qualifying and the race, clawed its way back to 15th.

The lone LMP675 entry from Dick Barbour Racing at least made it to the finish, with Didier de Radigues, John Graham and Milka Duno taking 13th spot behind the best of the Cadillacs.

Corvette drivers Ron Fellows and Johnny O'Connell thus finished fifth overall, and took class honours after an enthralling GTS battle with the Konrad/Team Saleen works entry. In the end, the leading C5-R crew beat Corvette team-mates Andy Pilgrim and Kelly Collins by 5.3secs, but that statistic does little to convey the fight that ensued on track.

Despite its pace in qualifying, the Saleen could not out-run the two yellow Corvettes come raceday. Fellows dogged Terry Borcheller's every move right from the start, before making the most of the American's growing tyre problems to snatch the lead at around one-third distance. Once ahead, the Canadian Sears Point expert gradually pulled away, leaving Borcheller and team-mate Franz Konrad to fend off the advances of the second C5-R.

Once again, tyres played an important part in deciding the outcome of the battle, with the Saleen team's decision to go for the softer of two Goodyear compounds playing into Corvette's hands. With their rubber losing grip in half the time it took Chevrolet's harder compound, the S7R was eventually passed by the Pilgrim/Collins car for second in class, and faded to a 16th place finish, two laps down on the class winners.

The GT category was a story, for the first time, of BMW versus BMW. The ageing Porsche 911GT3s hardly got a look in as the new, and controversial, M3 GTRs romped away with the race, although the Munich works team did not have things all its own way.

For the first time this season, the American Prototype Technology Group got its hands on the latest version of the venerable M3 and showed that it was capable of matching the factory cars every step of the way. Bill Auberlen, a veteran of BMW's prototype campaign, opened out an early advantage, while the other cars shrugged off the advances of the few Porsches able to run with them in the opening stages, but eventually dropped back into the clutches of an evenly matched trio.

The first caution period somehow managed to reverse the BMWs' positions, with Jorg Muller's works car coming out at the head of the pack and Auberlen's co-driver, Niclas Jonsson, running fourth after the first round of driver changes. BMW, by now, had things all their own way, with the best of the Porsches a lap down, and championship aspirant Randy Pobst's Alex Job example plagued by throttle problems that would drop it well down the order.

Just as things looked settled at the head of the pack, however, there was an incident involving one car from either BMW camp. Although the quartet had swapped paint and places throughout, Fredrik Ekblom's works machine forced its way past Hans Stuck's PTG example, dropping the veteran a place in the final order. The Swede was penalised and placed on probation for causing an 'avoidable incident', the stewards' decision dropping him behind Stuck in the final order.

GT victory went to former Formula One and CART driver Lehto and team-mate Jorg Muller, who helped inflict Porsche's first ever defeat in the ALMS class.

The best Stuttgart could manage was fifth in class, and eleventh overall, in the hands of Alex Job's second car, driven by Sascha Maassen and Lucas Luhr. Britain's Johnny Mowlem, along with new team-mate Timo Bernhard and team owner Michael Petersen finished sixth in class and 14th overall.