At the front of the race for 145 kilometres after making it into the 26-rider move of the day in the crosswinds, Sagan sat patiently six wheels back behind Giacomo Nizzolo whose Italian team mate Jacopo Guarnieri opened up the sprint with one kilometre to go.
"I don’t believe it. I’m still in shock," Sagan said. "I'm very happy because there was a crosswind and I was the last one to make the first group.
"There was a bit of a headwind so I felt I needed to come from the back. I felt I was lucky because Nizzolo didn’t close me out. If he closed me out for sure we would have crashed because I wasn’t going to brake. We should have crashed but I’m happy. It’s unbelievable."
Sagan's second rainbow jersey in a row also tops off an almost perfect year for the Slovakian. Since the road world championships in Richmond, USA last year, Sagan has claimed 14 victories, including three Tour de France stage wins, the Tour de France green points jersey, and the Gent-Wevelgem and Tour of Flanders double.
This prestigious victory and impressive palmares must surely go a long way to prove he is the best rider of his generation.
As it happened
The peloton allowed a group of seven riders to pull clear soon after the flag dropped. Brayan Ramirez (COL), Nick Dougall (RSA), Natnael Berhane (ERI), Ryan Roth (CAN), Anas Ait El Abdia (MOR), Sergiy Lagkuti (UKR) and Rene Corella (MEX) quickly built up a maximum lead of over 11 minutes after just 30 kilometres.
The peloton meandered behind until it hit the first cross wind section with 200kms to go where tensions began to rise. Once the riders turned and headed to the second cross wind section with 178kms to race, the Belgian team struck, driving the pace.
Cracks instantly appeared. Australians Michael Matthews, Luke Durbridge and Matt Hayman made the group with six Belgians (including Boonen, Jasper Stuyven, Oliver Naesen, Jurgen Roelandts, and Greg Van Avermaet) along with Sagan, Cavendish, Alexander Kristoff, and Edvald Boasson Hagen.
Andre Greipel and Nacer Bouhanni were caught in a large group a minute adrift with as many as 11 echelons further behind.
The wind caused havoc in other ways, blowing Ramirez off the road who made it back to the break. Meanwhile, Durbridge crashed out along with favourite Fernando Gaviria (Colombia) and Durbridge's Orica BikeExchange teammate Luka Mezgec.
The Belgian group made the catch with 145kms to go, the breakaway spending 100kms off the front.
Earlier, Caleb Ewan found the pace too hard falling out the back after the Belgians turned the screws and abandoned the race once he reached the pearl circuit.
But the 22-year-old joined an illustrious field of abandons including Great Britain's Geraint Thomas, Steven Cummings, and Ian Stannard, all hardened classics riders. Only 53 riders out of 199 starters finished the race.
After two laps of the finishing circuit, the gap back to Greipel's group was one minute and 50 seconds. Team-mate Degenkolb desperately tried to motivate the chase for his leader but received no real cooperation from the riders with colleagues up the road.
His frustrations boiled over when he squeezed water in the face of Belgian Jens Debusschere who refused to work in Greipel's group. Degenkolb was heard on the coverage to say "I am chasing for your trade team-mate," meaning Lotto-Soudal's Andre Greipel.
Ultimately Degenkolb too abandoned while Greipel finished the race over five minutes behind Sagan. 
Mark Cavendish (L), Peter Sagan (C) and Tom Boonen. Source: Supplied
