The Lotto-Belisol rider went clear of the chasing pack led by Norwegian Alexander Kristoff (Katusha) and German Marcel Kittel (Argos-Shimano).
Bak adds the race, which has been held in the Fourmies commune of France since 1928, to his stage 12 win on the Giro d'Italia.
He is also a former national road race and time trial - three times - winner.

