The Slovakian, the world and European road race champion, won the fourth leg of the race from Aalter to St-Pieters-Leeuw in Belgium after pipping German Lotto-Soudal rider Andre Greipel on the line.

Tinkoff rider Sagan lunged for the line to successfully back up his win on stage three yesterday, which took the peloton from Blankenberge to Ardooie.

He survived contact with Arnaud Demare in the final stages and admitted afterwards that he wasn't sure he had won.

Andrei Grivko and Dmitriy Gruzdev, both of Astana, had attempted a two-man break but were eventually caught.

Norway's Alexander Kristoff, riding for Team Katusha, finished third today as a host of riders finished on the winner's time of 4hr 42mins 12sec.

"Today was about timing and good positioning," said Sagan, who won the inaugural European Road Cycling Championships road race crown in Plumelec in France on Sunday (September 18) and the world title in Richmond last year.

"I was lucky again with that."

The bonus seconds gained by the 26-year-old have seen him assume the race leader's white jersey from Australia's Rohan Dennis, with the BMC cyclist now seven seconds adrift of Sagan's overall time of 13hr 17mins 29sec.

Dutch rider Jos van Emden of LottoNL-Jumbo is third overall, 12 seconds behind the Slovakian. 

The fifth stage of the International Cycling Union (UCI) WorldTour race tomorrow will see riders return to The Netherlands for a 20.9 kilometre team time trial, starting and finishing in Sittard-Geleen.