The Belgian looked in good shape for most of the race, constantly near the front of the peloton at key sections and looked set to compete in the finale of the Italian Classics.
With the peloton just a handful of seconds behind the trio of Simon Gerrans (GreenEdge), Fabian Cancellara (RadioShack-Nissan) and Vincenzo Nibali (Liquigas) on the descent of the Poggio, Boonen was caught behind a crash, and unable to regain contact with the chase group. He eventually crossed the line in 22nd place.
"I had really good legs, maybe the best legs ever in Milano-San Remo," Boonen said. "It was always under control and the team did a really good job for me. They kept me in the first 10 to 15 positions in all important moments of the race. Then on the Poggio I was 7th or 8th when we took the corner to go downhill.
“I was really good, the team was with me, and we were in good position ready to fight for victory. Then, in the first part of the downhill a rider crashed, and I was just behind him. I had to brake, and lost 100 meters.
“Because of that it was impossible to come back.”
Despite the setback, Boonen and his teammates will look to regroup ahead of the remaining spring classics, where the Belgian will hope to feature in the Tour of Flanders and Paris-Roubaix.
“In any case I am in good shape and I am ready to fight for the next races in the coming weeks."