Citroen's Jose Maria Lopez produced a fearless, attacking drive from last on the grid to take a sensational second victory of the World Touring Car Championship season at Paul Ricard.
The triple TC2000 champion was relegated to the back of the grid when a valve controlling an automatic fuel shut-off safety system was found to be non-functioning after qualifying.
The Argentinean had already fought past Citroen team-mate and 10th-placed starter Yvan Muller by the end of the first lap to run seventh.
Muller stayed in close pursuit of Lopez to finish second, 1.886 seconds adrift at the chequered flag.
"I didn't expect this," said Lopez. "Obviously that makes it more satisfying than when you win from pole."
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Early leader Tiago Monteiro saw a 4.8s lead negated by the appearance of the safety car on lap five, when some tyres marking a corner apex were knocked onto the track.
By this stage, Lopez had risen to second, ahead of Muller, Monteiro's factory Honda team-mate Gabriele Tarquini and polesitter Mehdi Bennani's Proteam Honda.
Monteiro maintained his lead over Lopez on the restart, which lasted just half a lap before the safety car was required again.
At the tail of the field, TC2 rookie John Filippi had clouted an Engstler BMW at Turn 1, bringing his damaged Campos SEAT to a halt in the middle of the road.
The race went green on lap nine, and Monteiro survived in front for just one further lap before Lopez scythed through under braking for the fast, right-hand, Signes corner.
"I have to thank Yvan for giving me a lot of respect when I was challenging Tiago Monteiro," said Lopez. "He could have very easily hit me, so thank you to Yvan."
Muller immediately followed suit, diving past Monteiro into the Double Droite du Beausset. Ex-Formula 1 driver Monteiro held third to the finish.
After his race one podium, Monteiro's team-mate Tarquini had the dubious honour of being passed by Lopez around the outside of Chicane Nord after overshooting the corner and came home fourth.
Bennani completed a trio of Hondas in the top five in fifth, ahead of the battle-scarred third Citroen of Sebastien Loeb.
The nine-time World Rally champion had a highly eventful race. Loeb was involved in a brush with team-mate Muller at the final corner in the early stages, and suffered further contact when the door was slammed on the front of his C-Elysee by Campos Chevrolet driver Dusan Borkovic at Turn 1.
Gianni Morbidelli recovered to ninth after being tagged into a spin by Tom Chilton on the opening lap. Chilton would serve a drive-through for the incident.
It was amid the midfield confusion resulting from this incident that Lopez was able to put his critical pass on Muller.
Results - 18 laps:
Pos Driver Team/Car Time/Gap
1. Jose Maria Lopez Citroen 30m24.551s
2. Yvan Muller Citroen +1.886s
3. Tiago Monteiro Honda +7.994s
4. Gabriele Tarquini Honda +8.459s
5. Mehdi Bennani Proteam Honda +17.407s
6. Sebastien Loeb Citroen +17.924s
7. Dusan Borkovic Campos Chevrolet +18.592s
8. Norbert Michelisz Zengo Honda +18.927s
9. Gianni Morbidelli Munnich Chevrolet +20.531s
10. Hugo Valente Campos Chevrolet +21.787s
11. Rob Huff Lada +22.216s
12. Rene Munnich Munnich Chevrolet +23.391s
13. James Thompson Lada +25.800s
14. Mikhail Kozlovskiy Lada +26.475s
15. Tom Chilton ROAL Chevrolet +41.250s
16. Franz Engstler Engstler BMW +44.222s*
17. Pasquale di Sabatino Engstler BMW +46.048s*
John Filippi Campos SEAT 9 laps*