Nathanael Berthon fought off intense pressure from British Formula 3 champion Daniel Ricciardo to claim his maiden Formula Renault 3.5 victory at Magny-Cours.
In a chaotic rain-hit race, a pre-race shower wrong-footed many teams and multiple drivethrough penalties were awarded for late tyre changes on the grid.
Ricciardo was among six drivers to receive a penalty, but took plaudits for a superb recovery in which he finished just 0.250 seconds behind Berthon at the flag.
"I was told on my radio, when it started to rain again in the middle of the race, that I had a six second gap to Ricciardo and to manage it," said Berthon. "About two corners later I saw him in my mirrors and thought, 'I'd better push a bit more.'"
Double Brno polesitter Filip Salaquarda finished in third place for ISR, the Czech losing second to Ricciardo after running wide at Grande Courbe on lap 17.
Championship leader Mikhail Aleshin had mounted a strong challenge to Berthon's lead over the first half of the race, but was caught out by a downpour 10 laps from the finish and ran through the gravel trap at the Melbourne hairpin. The delayed Aleshin would take fourth spot.
Albert Costa benefited from a last lap problem for Salaquarda's ISR team-mate Esteban Guerrieri to seize fifth position.
From 22nd on the grid, European Formula 3 Open champion Bruno Mendez correctly chose slick tyres for his FHV Interwetten machine and rose to a season best finish of sixth. The result was a welcome turnaround for the Spaniard, who was unable to take part in second practice on Friday after suffering a sizeable shunt in the morning session.
The pre-race shower led to the start being delayed, but with the rain stopping quickly the majority of the leading runners opted to start on slicks. Ricciardo, Berthon and Aleshin staged a breakaway over the early laps, as the drivers on dry tyres lapped around 10 seconds faster than those on wets.
Brendon Hartley and Daniil Move, who were both forced to start from the pitlane after technical trouble on the grid, Guerrieri, Ricciardo, Costa and Jon Lancaster (on wets) were all handed penalties. Such was the advantage afforded by the dry tyres, and the relatively short nature of the Magny-Cours pit lane, that Ricciardo was soon back in contention after taking his drivethrough on lap six.
The Australian rejoined in third place, while Berthon made his pitstop from the lead two laps later. Ricciardo had a six second advantage over Berthon at this point, with his own mandatory tyre change still to be made. Salaquarda, who had not stopped at all, held the lead.
"It was a crazy race for a number of reasons, not just the weather," said Ricciardo. "After the penalty I was a bit disappointed, and I rejoined not knowing where I was. After the stops, though, I saw P4 on my board and thought they must mean P14, but I realised then that I had a shout of a podium."
Once the pitstop sequence had played itself out, Ricciardo reeled in a seven second deficit to Berthon but was unable to find a way by.
Aleshin now leads the championship with 75 points, nine ahead of Ricciardo, with Guerrieri third on 59.
Pos Driver Team Time/Gap 1. Nathanael Berthon Draco 46m04.729s 2. Daniel Ricciardo Tech 1 + 0.250s 3. Filip Salaquarda ISR + 13.237s 4. Mikhail Aleshin Carlin + 20.746s 5. Albert Costa Epsilon Euskadi + 22.419s 6. Bruno Mendez FHV Interwetten + 55.547s 7. Stefano Coletti Comtec + 55.975s 8. Sten Pentus Fortec + 57.642s 9. Esteban Guerrieri ISR + 1m05.435s 10. Nelson Panciatici Junior Lotus + 1m07.159s 11. Daniel Zampieri Pons + 1m17.892s 12. Greg Mansell Comtec + 1m18.199s 13. Jake Rosenzweig Carlin + 1m19.560s 14. Sergio Canamasas FHV Interwetten + 1m28.683s 15. Victor Garcia KMP + 1 lap 16. Walter Grubmuller P1 + 1 lap 17. Jan Charouz P1 + 1 lap 18. Keisuke Kunimoto Epsilon Euskadi + 1 lap 19. Julian Leal Draco + 2 laps Retirements: Brendon Hartley Tech 1 22 laps Federico Leo Pons 21 laps Anton Nebylitskiy KMP 17 laps Jon Lancaster Fortec 12 laps Daniil Move Junior Lotus 0 laps