Nico Hulkenberg took a fine win in pouring rain – but he may lose the victory as the stewards began an investigation into whether he had made a pass under yellow flags.
Championship duellists Sebastian Buemi and Romain Grosjean were second and third.
James Jakes made a poor start from pole position on a damp track. While he tried to cover an attack from second-placed Yelmer Buurman, Hulkenberg mugged the pair of them and shot into the lead.
Jakes slipped back to fourth while Hulkenberg made his escape. Yann Clairay moved into second but Buurman quickly passed him.
Clairay then ran wide on the damp circuit and hit the barrier nose-first, tearing his front wing off. He limped into the pits and took the opportunity to switch to wet tyres as the rain got heavier.
That left Jakes third ahead of Romain Grosjean, but the Frenchman made a bold move around the outside of Tarzan to grab the place.
Buurman managed to get Hulkenberg’s lead down to under a second by lap seven. By now the rain was really picking up and Jakes pitted for wet weather tyres.
It looked like a smart move as the remaining drivers on slick tyres were crawling into the pits, and Kobayashi spun off into the barriers.
Hulkenberg pitted from the lead on lap eight but Buurman stayed out, hoping the rain would ease. Staying out gave him a lead of almost 50 seconds, but Hulkenberg cut seven seconds out of that on his first flying lap.
But the rain continued to fall and Buurman ran very wide on lap 14. Hulkenberg took the lead off him and Buurman began to slip down the order. He lost second place to Sebastien Buemi and third to championship leader Grosjean .
Now Buemi set off after Hulkenberg, taking seconds off him on each lap as the German struggled in traffic. With eight minutes left the gap was a little over five seconds.
The rain got heaver with every lap and Buemi’s progress towards Hulkenberg came to a halt, partly thanks to Cyndie Alleman, who held the Swiss up for several laps.
Hulkenberg’s lead was back up to over eight seconds by the time he took the chequered flag for his second win of the year.
Buemi was comfortably second ahead of Grosjean, with Tom Dillman, Renger van der Zande and James Jakes completing the points-scoring top six. Buurman’s gamble failed, leaving him 16th.