The Rapax driver inherited pole when DAMS' Felipe Nasr picked up a penalty after Friday's feature race, and Dillmann made the most of his good fortune. He made a perfect start, held the lead into the first corner and then set about eking out an advantage.
Initially iSport's Marcus Ericson gave chase, but as happened in the feature the Swede was unable to build upon an excellent start and he was soon passed by Arden's Luis Razia.
In the closing stages the Brazilian started to take sizeable chunks out of Dillman's lead, but the Frenchman had just enough of an advantage to hold on.
Davide Valsecchi fell two places short of making GP2 history by winning four races on the bounce. The DAMS star was delayed when Caterham's Giedo van der Garde was tipped into a spin by Lotus's Esteban Gutierrez at the first corner of the opening lap and then spent too long finding a way by the ailing Ericsson, who had damaged his front wing when he hit an errant polystyrene brake marker board.
Gutierrez made up for a terrible performance by Lotus in the feature event by holding on to fourth, ahead of Carlin's on-form Rio Haryanto. Nasr worked his way up to sixth while Ericsson clung on to seventh.
Racing Engineering's Fabio Leimer claimed the final point after a last-lap pass on Coloni's Fabio Onidi.