Simon Gerrans made it consecutive Australian victories in the Milan-San Remo classic as Mark Cavendish failed to finish.
The Australian national champion edged Switzerland's Fabian Cancellara in a thrilling sprint finish.
Cavendish, 26, and his Team Sky colleagues called time on their chase 48 kilometres from the end.
GreenEdge rider Gerrans was part of a three-man pack that hit the front with six of the 298km remaining.
Cavendish was never in contention for a repeat of his 2009 Milan-San Remo win and first dropped behind the peloton on the mild Le Manie climb 97km from the finish line.
Colombian rider Carlos Julian Quintero briefly lost consciousness after a crash at the bottom of the Le Manie descent with 85km left of the event. The Colombia-Coldeportes rider was tended to by paramedics on the side of the road.