The 31-year-old, racing for BMC, finished 2min 34sec ahead of his compatriot Thomas de Gendt after the 216 kilometre leg to claim the famous yellow jersey from Peter Sagan.

He came home in 5hr 31mins 36secs to bag the second Tour de France stage win of his career.

Today's leg was the first in the mountains during this year's race, with Van Avermaet taking his place in a nine-rider break early in the stage.

The Belgian then launched an attack and dropped his only challenger, Lotto Soudal's de Gendt, before the penultimate climb.

Van Avermaet is not thought to be a contender for overall honours but began only 18 seconds behind Sagan so easily took yellow.

The favourites eventually picked up the pace to prevent Van Avermaet's lead from becoming even bigger with Britain's defending champion Chris Froome and Colombia's Nairo Quintana among those to finish in the peloton.

Movistar's Quintana, twice a runner-up to Team Sky's Froome, attempted to create distance between his rival in the closing stages but the Briton and his team were able to respond.

France's Etixx-Quick-Step rider Julian Alaphilippe is now second in the general classification, 5min 11 sec behind Van Avermaet.

Spainish Movistar cyclist Alejandro Valverde is third, 5min 13sec adrift.

Froome and Quintana are both 5min 17sec behind.

The Grand Tour will continue tomorrow with a 190.5km stage six from Arpajon-sur-Cere to Montauban.