The first stage took the riders 198 kilometres through the Ardennes from Liège to suburban Seraing. The uphill finish ruled out a bunch sprint. The final climb was too steep for many sprinters, including Mark Cavendish.
Race leader Cancellara (Radioshack) attacked and only 21-year-old Sagan could follow the Swiss ace. Norway's Edvald Boasson Hagen was able to close the gap a bit later, and the 3 sprinted for the day's prize. Sagan (Liquigas) beat Cancellara and Hagen with ease.
Philippe Gilbert came 4th, the Fleming Dries Devenyns 10th. The Belgian Lotto team had put everything on Fleming Jelle Vanendert, but the plan didn't work and Vanendert was never in contention for the flowers.
Cancellara, the winner of yesterday's prologue time trial, retains the yellow jersey, leading Bradley Wiggins by 7 seconds. The second stage on Monday takes the riders to Tournai (Doornik), just south of East Flanders.