He moved into first after pressuring Jorg Muller into a mistake and pulled out a substantial lead after a safety car period to win.
Priaulx slotted in behind Muller at the start and the two rear wheel drive BMWs easily pulled away from the chasing pack.
Augusto Farfus made a rocket of a start from ninth place to pass both Alain Menu and Rob Huff’s Chevrolets.
But the combination of Farfus’s maximum success ballast and Chevrolet’s weight break meant that Menu and Huff were both past Farfus in no time. This left Farfus outside of the points places once again.
On lap two Gabriele Tarquini took a look at Yvan Muller for fourth place – but he lost momentum and Nicola Larini’s Chevrolet passed him. Larini then caught Muller, forcing the Frenchman to defend.
Tarquini ran wide on the fourth lap allowing Menu past – Huff would have followed his team mate through had Tarquini not pulled across to block him.
At the same corner the next time around Priaulx’s pressure on Jorg Muller forced a mistake – the German locked up and his team mate was past in an instant. Larini meanwhile passed Yvan Muller and set after Tom Coronel’s third-placed Seat.
Menu also got past the Seat but Huff’s efforts to pass Muller were thwarted by the arrival of the safety car. Miguel Freitas had clipped the wall at the fast chicane and hit the barrier hard with the front right corner of his Alfa Romeo. Fortunately he escaped injury.
Behind the safety car Priaulx led Jorg Muller, Coronel, Larini, Menu, Yvan Muller, Huff and Tarquini – with Farfus still ninth. As in the first race the distance was extended to 13 laps.
The restart came on lap 10 but while Priaulx made a faultless getaway behind him team mate Muller started slowly and a chasing pack of Coronel, Larini, Menu and the rest darted around behind the BMW.
Huff made a mistake and Tarquini tried to re-pass him but couldn’t -and that allowed Farfus through into eighth place for a vital point.
The Briton made another mistake on the penultimate lap as he made another bid to pass Yvan Muller but locked his wheels and hit the barrier head-on. That promoted Farfus to seventh.
Coronel’s hopes of a podium place were dashed on the final lap when Larini passed him and delayed the Dutchman, allowing Menu to pass as well – but then Larini crashed at the next corner.
Priaulx broke his 2007 victory duck to recover the crucial points lost at Brno. Jorg Muller fiinshed second and Menu returned to the podium for the second race in a row with third.
Coronel finished fourth ahead of Yvan Muller and Farfus a fortunate sixth. Tarquini was seventh and Pierre-Yves Courthals took the final point.
The drivers’ championship is now led by Jorg Muller with 58 points, with team mates Farfus and Priaulx on 56. The series moves on to Anderstorp in Sweden next.