[2] Davide Valsecchi was declared the 2012 series champion after he out-scored title rival Luiz Razia in the feature race.
It wasn't until lap 14 that Canamasas returned to the pits with a mechanical problem and retired from the race, but he had no idea that he had been disqualified.
Meanwhile, at the front, van der Garde held on to the lead after the restart and won easily by 1.7 seconds.
There was a fight for third place on the last lap when Fabio Leimer overtook Razia in turn ten, taking advantage of his rival's tire problems.
Davide Valsecchi and Felipe Nasr secured the DAMS squad's first teams' title in GP2 with fifth and seventh placed finishes enough to beat rival Lotus GP.