Gilbert saw off compatriot Tom Boonen and Slovenia's Borut Bozic in a three-man dash for the line with Italian Filippo Pozzato beating Spaniard Oscar Freire into fifth some 20sec off the leading trio.
For Gilbert the win brought a measure of revenge after Boonen pipped him to the Belgian championship in June.
Gilbert, 27, made his move for glory after another Belgian, Greg Van Avermaet, ran out of steam some 8km out along with Dutchman Tom Veelers, who had been instrumental in the formation of a ten-man escape at the 9km mark.
The champion, who cut his teeth with Franaise des Jeux after turning pro in 2003 before joining Silence only this year, won a stage of the Giro in May and then placed sixth at the world championships and also won Thursday's Coppa Sabatini Italian semi-classic.
His growing reputation sits well with a man who hails from Verviers in eastern Belgium and which is one of the strategic venues on the famed Liege-Bastogne-Liege route.
"I knew right from the off that I had a big sprint in me if I found myself in the mix to win it", said Gilbert.
"I have always said I fear no one in the sprint when it comes down to a tough race," he added, paying tribute to his teammates for responding in style in the escape to set up his triumph.