The Lotto-Belisol rider sprung out of an eight-man lead group at the end of the 165.8km route from La Louviere to Menin.
Guillaume Van Keirsbulck (Omega Pharma-Quick Step) and Maarten Wynants (Rabobank) completed the podium.
Michel Kreder (Radioshack), David Boucher (FDJ), Roy Curvers (Argos-Shimano), Stijn Neirynck (Topsport Vlaanderen) and Vladimir Isaichev (Katusha) attacked after 30km and built up a maximum lead of 3:55.
The peloton split with around 70km remaining and the speed of the group saw the escapees soon swept up - but the two bunches regrouped with 35km left.
However with 20km remaining, a new 25-man lead group formed from which eight men broke clear and the octet - also featuring Juan Antonio Flecha (Sky), Karsten Kroon (Rabobank), Benoît Vaugrenard (FDJ), Michael Schar (BMC) and Sep Vanmarcke (Garmin) finished 39 seconds clear of the chasers.
The stage was marred by numerous crashes and Team Saxo Bank's Takashi Miyazawa was sent to hospital with a suspected broken foot.
The four-stage race concludes on Sunday with the GC usually claimed by sprinters with Tyler Farrar, Adam Blythe and Robbie McEwen winning the last three editions.