Formula 1 World Championship leader Jenson Button and countryman Lewis Hamilton have both retired from the Belgian Grand Prix on the opening lap, after being caught up in a chain reaction m?l?e that caused chaos at Spa-Francorchamps.

Having qualified a lowly 14th - already dealing a blow to his title hopes - Button's ailing advantage in the drivers' standings is now likely to be further reduced after the British star found himself tagged from behind by Renault rookie Romain Grosjean, spinning the Brawn GP across the track, into the circuit barriers and out of contention. The first time the 29-year-old has not finished a race all year, it could scarcely have come at a worse moment.

In the ensuing chaos, McLaren-Mercedes ace Hamilton too received a whack from the rear and was spun into the barriers, in company with Scuderia Toro Rosso's Jaime Alguersuari, with the pile-up bringing out the safety car.

When the race resumed, Kimi Raikkonen made short work of powering his Ferrari past Force India pole-sitter Giancarlo Fisichella and into the lead, as Rubens Barrichello, Jarno Trulli and Adrian Sutil all endeavoured to recover ground after pitting for repairs.