Poland's Michal Kwiatkowski continued his outstanding start to the season by claiming the biggest one-day win of his career at Strade Bianche in Italy.
The 23-year-old Omega Pharma - Quick-Step rider broke away from a vastly reduced front group alongside Cannondale's Peter Sagan around 22km from the finish and then dropped his Slovak rival on the day's final climb inside the last 1km.
With the gradient kicking up to 16 per cent, Sagan injected a burst of pace in the middle part of the 800m ascent, but he soon ran out of steam and Kwiatkowski, still looking fresh, had little trouble overtaking him and then riding away to an 19-second victory.
Alejandro Valverde (Movistar) took third place, a further 17 seconds back, after forming part of a four-man chase group.
Kwiatkowski's triumph follows previous wins this year at the Trofeo Serra de Tramuntana one-day race in Mallorca and on two stages of the Volta ao Algarve, where he also topped the general classification.
He revealed a reconnaissance of the finish in Siena on Friday had proved instrumental in defeating Sagan, who has now finished runner-up at Strade Bianche in each of the past two years.
"I didn't expect to drop him," Kwiatkowski said. "I knew the final pretty well from yesterday. He started slowing down a little bit and I saw that he was really suffering. So I went full gas until the end and that is how it was won. I'm pretty surprised as this is probably my best, most emotional victory so far."
Strade Bianche takes place over 197km in Tuscany and includes ten sections of punishing gravel road, after which the race is named.
Sagan initiates breakaway
With the day's initial four-man breakaway almost caught, the peloton was blown apart around 50km from home on the long and hilly seventh gravel section, resulting in an elite lead group of 23 riders forming at the head of the race.
That bunch fractured twice over the next 25km as several riders tried and ultimately failed to break clear, but then Sagan launched a piercing attack 22km out and only Kwiatkowski could follow.
The duo quickly built up a gap of 20 seconds with 19km to go and after further stretching it to 48 seconds with 15km remaining, it became evident that they would not be caught.
With the decisive ascent of Via Santa Caterina waiting in Siena and Kwiatkowski a superior climber, Sagan tried to conserve as much energy as possible, even emptying his pockets of all weight, but he wilted quickly on the steep slope and had no answer to Kwiatkowski's surge.
1 Michal Kwiatkoswki (Pol) Omega Pharma - Quick-Step, 5:20:33
2 Peter Sagan (Svk) Cannondale, +19secs
3 Alejandro Valverde (Spa) Movistar, +36
4 Damiano Cunego (Ita) Lampre-Merida, +40
5 Roman Kreuziger (Cze) Tinkoff-Saxo, same time
6 Fabian Cancellara (Swi) Trek Factory Racing, +59
7 Cadel Evans (Aus) BMC, +1:44
8 Warren Barguil (Fra) Giant-Shimano, +2:02
9 Wout Poels (Ned) Omega Pharma - Quick-Step, +2:11
10 Simon Geschke (Ger) Giant-Shimano, +2:51
16 Ian Stannard (GB) Team Sky, +3:16
View the best photos from Strade Bianche here