Rising Australian star Caleb Ewan has finished a close second to Vincenzo Nibali, with the 2014 Tour de France champion claiming the Milan-San Remo "Monument" classic.
Nibali just held off the sprint specialists over 291km on Saturday, on a day when Mark Cavendish suffered a heavy crash towards the end of the stage.
Nibali snatched the first of five top one-day races - Milan-San Remo, Tour of Flanders, Paris-Roubaix, Liege-Bastogne-Liege and Tour of Lombardy - by pulling away from the pack on the ascent of the Poggio, seven km from the finish.
The Bahrain-Merida rider, the first Italian to win the "Primavera" since 2006, looked back only in the final few metres when a group of top sprinters were breathing down his neck.
Ewan (Mitchelton-Scott) and France's Arnaud Demare (Groupama-FDJ), the 2016 champion, were second and third respectively.
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"I know it is still a massive result to finish in second place but to be so close to the win is a little bit disappointing," said Ewan, who will make his Tour de France debut later this year.
"To be honest I was just thinking of doing my own sprint and if we caught Nibali, we caught him, if we didn't, we didn't.
"I was just focusing on my sprint as there were still good sprinters there and I knew it would be tough to beat those guys.
"My team put me in a good position on both the Poggio and Cipressa so I didn't need to fight too much.
"After this year I know I can potentially win this race so I can come back next year and the year after and try to win."
Briton Cavendish (Dimension Data) suffered a spectacular crash, landing on his back after somersaulting after hitting a central divider.
Nibali eventually prevailed by a bike length, becoming the first grand-tour champion to win the race since Sean Kelly in 1992.
