Poland's Michal Kwiatkowski stunned world champion Peter Sagan in a thrilling three-up sprint to win the 108th Milan-San Remo on Saturday.
Kwiatkowski, the 2014 world champion, claimed his first 'La Classicissima' after launching his sprint late to stun Sagan at the finish in San Remo.
Frenchman Julian Alaphilippe (Quick Step) finished close behind to claim a well-deserved podium place on his debut after 291 km of racing from Milan.
"I'm very happy, although I actually didn't expect to win," said Kwiatkowski, who had been scheduled to work for teammate Elia Viviani and help set the Italian up for a winning sprint.
"I won Strade Bianche recently, and now to come and win 'La Primavera' is just ... incredible."
Fresh from winning two stages in commanding fashion at Tirreno-Adriatico, Sagan started Milan-San Remo as the man to beat from a quality-packed sprint field that included 2014 champion Alexander Kristoff, 2015 winner John Degenkolb and Frenchman Arnaud Demare, who stunned the field to triumph last year.
Kristoff went on to finish fourth at five seconds in arrears and at the head of a chasing bunch featuring Colombian fast man Fernando Gaviria, Demare, Degenkolb, Frenchman Nacer Bouhanni and Viviani.
But despite leaving all his pre-race rivals behind after a decisive attack on the Poggio climb six kilometres from the finish, Sagan suffered the misfortune of taking Kwiatkowski with him when the Pole counter-attacked with Alaphilippe.
A "long" sprint on the home straight then left the Slovakian short of juice in the final metres when Kwiatkowski appeared from behind his wheel to snatch victory at the line.
"He actually made the race," Kwiatkowski said when asked about Sagan's performance. "But when he escaped, I knew we absolutely had to catch him."
Having built a decisive lead on the chasing peloton during the technical descent towards the final, flat two kilometres, Sagan led into the final kilometre.
But the Bora team rider took the risk of launching his sprint nearly 350 metres from the finish, giving Kwiatkowski the chance to follow his wheel and overtake him in the final metres.
The pair almost crashed as an off-balance Sagan wavered, but there was a quick handshake. Sagan and Kwiatkowski have been beating each other on and off for the best part of 10 years.
It was Sagan's second runner-up place after his second behind Germany's Gerald Ciolek in 2013, but in trademark fashion he brushed off the defeat.
"I've got used to second here, though I was expecting something different," said Sagan, who is famous for pulling 'wheelies' while riding up the climbs of the Tour de France.
"The final went as it did. Both of them took relays with me, but I thought I had the legs to go for a long sprint.
"The results don't matter. It's important to give the fans a bit of a show."
On his maiden appearance at the first 'monument' of the cycling classics season, Alaphilippe came off worse for wear after over seven hours of racing.
And he was just as surprised as Kwiatkowski at finishing on the podium.
"I'm very happy, to come here and make the podium is incredible."