McLaren Formula One driver Jenson Button of Britain celebrates after winning the Belgian F1 Grand Prix in Spa Francorchamps September 2, 2012.  [Photo/Agencies]

SPA-FRANCORCHAMPS, Belgium - McLaren's Jenson Button won the Belgian Grand Prix from pole position on Sunday after a first corner carnage ended the hopes of team mate Lewis Hamilton and Ferrari's Formula One leader Fernando Alonso.

Lotus Formula One driver Romain Grosjean (R) of France crashes with Ferrari Formula One driver Fernando Alonso (L) of Spain at the start of the Belgian Grand Prix in Spa Francorchamps September 2, 2012.  [Photo/Agencies]

Button enjoyed an untroubled afternoon in the Belgian sunshine, taking the chequered flag 13.6 seconds clear of Red Bull's double world champion Sebastian Vettel, who won from pole last year.

Finland's Kimi Raikkonen took third place for Lotus.

Alonso, who started the race with a 40 point lead over Red Bull's Australian Mark Webber, had hoped for a record-equalling 24th successive points finish but that was shattered in a cloud of carbon-fibre after a matter of metres.

His lead was cut to 24 points, with Vettel moving up to second overall. Webber dropped to third, 32 points adrift of Alonso.

The Spaniard could at least consider himself fortunate not to have been hit on the head by the flying Lotus of Frenchman Romain Grosjean, whose car took off after colliding with  Hamilton.

"It was a good start, then a big boom. I have not seen the image, but the main thing is we are all OK. I do not know if I moved over too quickly," said Grosjean.

Sauber's Sergio Perez also retired on the spot in a miserable afternoon for the Swiss team after a Saturday qualifying session that had promised so much with their cars on the front two rows.

Kamui Kobayashi, only the second Japanese driver to start from the front row, was also caught up in the first lap mayhem and went to the back of the field and finished 13th.

Button's 14th career win, and first at the classic Spa circuit, came in his 50th race for McLaren.

"This circuit is such a special one to most drivers, the way it flows and the history, so to get a light to flag victory is very special," said the 2009 champion after his second win of the season.

Force India's German Nico Hulkenberg came fourth, his team's best result of the season, ahead of Ferrari's Felipe Massa and Webber.

Seven-times world champion Michael Schumacher marked his 300th grand prix with seventh place for Mercedes after running as high as second at the circuit where he began his F1 career in 1991 and took his first win in 1992.

Toro Rosso pair Jean-Eric Vergne and Daniel Ricciardo were eighth and ninth in a strong turnaround for the little Italian team ahead of their home race at Monza next weekend.

The stewards were given plenty to ponder with a stack of incidents remaining under investigation and to be resolved after the race.

They included what looked like a clear jumped start from sixth place by Venezuelan Pastor Maldonado's Williams and the unsafe release from the pits of Webber's Red Bull.

Schumacher's cut across Vettel to get into the pitlane was also on their list.