Demare is the first French rider to win the opening monument of the season since Laurent Jalabert in 1995.
Coming off the final climb and with the peloton strung out, Sky's Michal Kwiatkowsi burst into the lead and stayed out in front until the final two kilometers.
The Pole was reeled in though by Swiss veteran Fabian Cancellera before Demare powered through to win.
Colombian Fernando Gaviria (Etixx-Quick Step) had looked in prime position to claim victory but crashed heavily and rolled across the line in tears.
World champion Peter Sagan was also in the mix but again failed to deliver a victory on one of the sport's classics.
A landslide had caused the race to be re-routed, with the riders sent on to the A10 motorway, before it reverted to the usual route that hugs the Italian coast.
Eleven riders formed a breakaway but Tinkoff and BMC drove the peloton which swallowed up the front-runners with 25km left.
The race was littered with crashes, one of which, with 30km remaining, took down Demare but he quickly recovered.
(Reporting by Martyn Herman, editing by Clare Fallon)
Share
