Jenson Button admits that he got off lightly as an early exit from the Belgian Grand Prix went largely unpunished by his Formula One world championship rivals.

Shrugging off a pre-race radio problem, the Briton had made a good start from his disappointing 14th grid slot, progressing up to eleventh and challenging Heikki Kovalainen into Les Combes, when the rear of his car was struck from behind by Romain Grosjean.

The contact not only turned Button into the barriers and removed Renault rookie Grosjean from the race, but also accounted for fellow Briton Lewis Hamilton and Spanish newcomer Jaime Alguersuari, after the McLaren man was collected as he attempted to avoid the melee.

"I had a really good start and had made up a few places in the first few corners to be ahead of Lewis and Rubens," Button recalled, "I had a good run going down the
straight to turn five just after Eau Rouge, and was on the outside of Heikki as I turned in for the corner. Quite simply, Romain outbraked himself and hit my back wheel , and that was it for my race today.

"It's frustrating as I was in a reasonable position, having made up some places and with a lot of fuel on board - but it's better to have my first retirement here, where I haven't been so competitive than when I'm running at the front."

While Button watched on from the sidelines, his three title rivals all endured differing fortunes, with outsider Sebastian Vettel gaining the most points, finishing third behind Kimi Raikkonen and Giancarlo Fisichella, but only moving up to third overall as Red Bull team-mate Mark Webber failed to score and Rubens Barrichello added only two to his tally after lapsing into anti-stall mode at the start and suffering a smoking engine over the closing laps.

"I have to be happy with seventh place and the two points really after such an eventful race," the Brazilian noted, having trimmed Button's championship lead to 16 points with five races remaining, "We should have had far more from today, but the problem with the clutch at the start took away any chance of a podium, which is frustrating for me and the team.

"We changed my strategy at the end of the first lap to fuel longer for the first stint, which was a good move and gave me the chance to get into the points, and I had fun in the race from then on - the move on Mark Webber at the Blanchimont bend was definitely one of the highlights. The oil leak gave us some worrying laps but I was able to manage the pace and bring the car safely home which was a big relief."

With team boss Ross Brawn vowing to learn from lessons of Spa, Button insisted that he was staying positive ahead of next month's Italian Grand Prix at Monza.

"We're determined get back on the track at the next race, and be more competitive there, at a track which should be quite good for our car," he claimed.