World Superbike series leader Jonathan Rea finished second to maiden winner Toprak Razgatlioglu in Saturday's first race of the weekend in France to extend his championship lead to 100 points.
The Turkish rider edged out Rea in a thrilling last-lap battle in a dramatic race which saw leader Michael van der Mark crash out with three laps left.
The Kawasaki rider won by 0.2 seconds from Rea, with Tom Sykes third.
Rea's title rival Alvaro Bautista came in fifth on his Ducati at Magny-Cours.
The Northern Irishman went into the weekend with a 91-point advantage, needing to out-score the Spaniard by 34 points over the three races to secure a record fifth successive crown.
That would give the Kawasaki rider an unassailable 125-point lead with two further rounds of the series to come in Argentina in mid-October and Qatar in late October.
"There were some crazy manoeuvres out there - the race never settled down. I made a big mistake on the last lap which gave Toprak a chance to make his race-winning manoeuvre. Congratulations to him," said Rea afterwards.
Razgatlioglu took his victory after starting from 16th place on the grid and becomes the first Turkish rider to ever win a World Superbike race.
If Rea wins the title he will better Carl Fogarty's tally of four WSB titles and equal compatriot Joey Dunlop's achievement of five consecutive Formula One world titles between 1982 and 1986.
Rea has won 11 races this season, including two at the last round in Portugal, with Bautista occupying the top step of the podium on 15 occasions.
The 32-year-old clinched double successes at Magny-Cours in 2018 and 2015 and picked up another victory in 2017.
Were he to win either of the two remaining races this weekend he will move above Noriyuki Haga as the most successful rider ever at the French circuit.
The 10-lap Superpole sprint race will be held at 10:00 BST on Sunday, with the second feature race three hours later.
Bautista won the first 11 races of the season to build a 61-point advantage over Rea but crashes at four consecutive rounds in Spain, Italy, Great Britain and the United States dealt a serious setback to his title chances.
|2019 WSBK Riders' Championship|
|Jonathan Rea (GB)||Kawasaki||510 pts|
|Alvaro Bautista (SPA)||Ducati||410|
|Alex Lowes (GB)||Yamaha||259|
|Toprak Razgatlioglu (TUR)||Kawasaki||248|
|Michael van der Mark (NED)||Yamaha||247|
|Leon Haslam (GBR)||Kawasaki||229|