Despite losing their pole-winning streak in qualifying for the sixth round of the American Le Mans Series at Portland, Audi maintained their dominance in the race when they eased to a 1-2 finish.

Having only managed third and fifth on the grid when the Dyson Lola received a weight break ahead of qualifying, Audi proved to have the stronger package in a race defined by excessive heat, with Allan McNish and Dindo Capello coming out top, while team-mates Frank Biela and Emanuele Pirro followed them on the lead lap, albeit 42secs adrift.

The result also proved a race record, with the Scot and Italian duo getting 142 laps under their belt compared to Biela and Pirro's 138 laps from the previous year.

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"I had total knowledge that it's an Audi. It doesn't fall apart," McNish said of the difficult conditions. "With this type of racing, anything can happen. The important factor was to keep ourselves in the game."

Nonetheless, Capello admits that the car was not ideal in the early part of the race following a scramble down to the first corner that resulted in him being hit.

"The big challenge for me was to stay on the track," he said. "After I got hit on the first corner, the car got really difficult to drive. I had a big oversteer going right. To be honest, I was really happy when we got the full-course yellow. I was doing so much time and was afraid to make a huge mistake. The car was really unpredictable. It really was a nightmare for me to drive."

It is their fourth overall win this year and their fifth LMP1 victory, leaving them to extend their lead over their nearest competitors to 39 points.

"It was a great race again," Capello said. "We should have won in Salt Lake City. Now we have won here. We knew that the Dyson and Porsche were really fast. We showed our car is fast and reliable, but in the first stint something made it really hard to drive so we made some changes when Allan got in the car. So it's great to see the car come around."

Having locked out the front row, the Dyson Lolas were unable to maintain their strong qualifying pace against the Audis, holding them off in first and third until the first round of pit stops when they were jumped.

Nonetheless, they proved reliable enough to cross the line two and four laps behind the Audis, with Chris Dyson and Guy Smith leading Butch Leitzinger and James Weaver.

Although most were expecting once again that the Penske Porsches would destroy its rivals in the LMP2 class, reliability woes would come to haunt the RS Sypder, with the ever dependable Intersport Lola of Liz Halliday and Clint Field duly taking advantage.

Good fortune and patchy reliability for the Penske Porsche pair of Sascha Maassen and Lucas Luhr meant Halliday and Field went into the race with a one point lead, even if there was little dispute as to who drove the faster car.

It was a lead Intersport were set to lose too when Maassen and Luhr stormed into the lead of the class and third overall following Romain Dumas' and Timo Bernhard's retirement with accident damage.

However, with just a few minutes remaining, the Penske Porsche was in the pit lane with a blown engine, leaving them to watch helplessly as Halliday and Field streamed past to take the class win.

"This one's for the team," said Halliday. "They are the ones who keep this Lola going around forever. Slow and steady wins the race has been our motto. We know we can't keep pace with the Porsches but they had some problems today that played into our favor. Great luck today."

However, their win, which also makes Halliday the most coveted female to compete in the series, only gives them a five point championship lead as Maassen and Luhr were still classified in second place.

Corvette Racing duly turned their GT1 pole position into victory, with Olivier Beretta And Oliver Gavin claiming their second win in a row in a faultless display of driving.

Gavin and Beretta, defending class champions, won by nearly a minute over the Aston Martin Racing DBR9 of Tomas Enge and Darren Turner. The two pairings sit 1-2 in the championship standings after six rounds, and Corvette Racing holds an 11-point edge over Aston Martin in the team championship.

"The car was very good. We tried to avoid the mess up in the chicane," said Beretta, who also posted the class' fastest race lap and is now a four-time winner at Portland. "I just took care not to make any mistakes. In the end, we managed to cruise. This is an unbelievable team. They work so hard."

The pole-sitting Risi Competizione Ferrari F430GT came from the rear of the field after a first-lap collision sent Jamie Melo to the pits, but, just as they did at Salt Lake City, Melo and Mika Salo returned from the back of the pack to record a hard-earned GT2 victory. The duo are the first pairing to win multiple times this season in the American Le Mans Series' most competitive class.

"It's not very good because we have to work a lot," said the pole-sitting Melo, who had another off near the 90-minute mark. "After we changed the tires, the car was working very well. We tried to push as much as possible. The team did a very good job as well. The Michelin tires worked very well, so the package is very good. The results are coming."

Salo made the winning pass on Patrick Long in the Petersen Motorsports/White Lightning Racing Porsche with 18 minutes remaining. Only a few laps earlier, Long pitted for a late splash of fuel but didn't take on fresh tires in hopes that the Michelins would hold up the remaining 25 minutes.

Long rejoined the race with a 1.38-second lead over the Ferrari. But Salo with fresher tires and traffic ahead of Long proved to be the difference. The Ferrari eventually finished 20 seconds ahead of the Petersen/White Lightning Porsche. In third was Bill Auberlen and Joey Hand in BMW Team PTG's No. 21 BMW M3, another 28 seconds behind.