Valentino Rossi's misjudged tyre strategy went largely unpunished in a chaotic San Marino Grand Prix won by Marc Marquez, as Jorge Lorenzo's title hopes were dealt a blow.

MotoGP championship leader Rossi did brilliantly to work his way to the front in a rain-affected race, but appeared to have left it too late to switch back to the slick tyres as the track dried out.

However, with Repsol Honda rider Marquez, who wrote off his title chances after failing to complete the British Grand Prix last time out, soaring clear, Lorenzo crashed out on lap 22 to offer his Movistar Yamaha team-mate a reprieve.

Rossi's miscalculation, on a newly re-laid surface that was yet to be tested in the wet, saw him finish down in fifth but he still managed to extend his overall lead by 11 points to the delight of a partisan crowd.

Monster Yamaha's Bradley Smith – one of the few to opt against a switch to wet tyres when the rain came – was rewarded for his bravery as he fought back from last place to eventually finish second, while third place went to Scott Redding of EG 0,0 Marc VDS, who had earlier slid off on lap six but timed his stops to perfection.

Marquez, who was part of an initial three-man breakaway with Rossi and Lorenzo, is now 63 points adrift of the championship lead with five races to come.