Priaulx’s rivals Jorg Muller and Augusto Farfus finished second and fourth respectively, meaning Farfus now leads the title race.
Felix Porteiro took his maiden win from pole in what look like a demonstration run for BMW – the German marque taking the top four places.
The rolling start produced chaos again. The lights were left on red for a long time which packed the field up very tightly.
Independent Pierre-Yves Courthals shot down the inside of the leaders from fifth on the grid and slammed into the side of second placed Andy Priaulx. Courthals continued but the championship leader was out.
Further around the first lap Tom Coronel and Luca Rangoni tangled and spun off – forcing the appearance of the safety car.
As the drivers queued up behind the safety car race control extended the race distance to 11 laps.
On lap three the race got underway again in orderly fashion. The BMWs maintained their advantage – pole sitter Felix Porteiro held on to his lead from Jorg Muller (up from seventh) and Augusto Farfus (from ninth).
Alessandro Zanardi made it four BMWs at the front, which cruised easily away from Nicola Larini’s Chevrolet, which had Yvan Muller and Gabriele Tarquini fighting hard to pass.
Zanardi in a weight-free BMW passed Farfus’s maximum ballast BMW for third on lap seven. But Larini comfortably maintained his advantage over the Seats and soon Alain Menu caught the battle for fifth.
But there were no other changes in the top eight and Porteiro cruised home to take his first WTCC victory.
WTCC championship standings after round 9
1. Augusto Farfus 45
2. Andy Priaulx 42
3. Jorg Muller 39
4. Yvan Muller 31
5. Nicola Larini 29
6. Gabriele Tarquini 23