Tadej Pogacar wins Strade Bianche after stunning 81km solo attack
The UAE Team Emirates rider went ahead on the 11.5km-Monte Sante Marie gravel section and never looked back, crossing the line two-and-a-half minutes clear of his nearest pursuers.
Toms Skujiņs (Lidl-Trek) was second with Maxim van Gils (Lotto-Dstny) in third place.
"We came to Sante Maria and the conditions were really tough. There was no more resources left in the group. It was a moment when it was really muddy and you couldn't see anything, so I decided to go on the attack," Pogacar said.
"I knew that it's going to be long but when I had a gap I knew I could go to the end."
The 215km race, one of the jewels of the Classics season, started and finished in Siena and included 15 gravel sections.
Last year's champion Tom Pidcock finished fourth.