Cavendish, who has a new book out called "Boy Racer", kept in contact on a mainly flat 176km and with 300m to go was led out by his team to take the victory in a time of 3.48.36.
He beat Alessandro Petacchi, Allan Davis, Robbie Hunter and Tyler Farrar with fellow Brit Ben Swift finishing eighth.
Rabobank's Dennis Menchov leads the General Classification by 34 seconds.