Julian Alaphilippe reclaimed the Tour de France's yellow jersey as fellow Frenchman Thibaut Pinot underlined his title credentials in Saturday's eighth stage.
Belgian Thomas De Gendt won the 200 km hilly stage from Macon from a breakaway, ahead of Pinot, the only rider able to follow Alaphilippe's brutal attack in the last climb with about 13 km left.
The French duo went full gas in the descent into St Etienne and held off a trimmed peloton at the finish.
They crossed the line six seconds behind De Gendt, but 20 seconds ahead of the bunch featuring defending champion Geraint Thomas, who suffered a scare 15 km from the finish when he took a minor tumble.
"I was ready for his attack since last night and all day I was waiting for it because I had great legs," said Pinot.
"It was a fantastic finale, it was beautiful to go together like this and we showed that we can work together even if we're in different teams," said Alaphilippe, whose move was highly expected as bonus seconds were up for grabs in the ascent to the Cote de la Jaillere and at the finish.
Alaphilippe now leads Italian Giulio Ciccone, who started the day in yellow with a six-second advantage, by 23 seconds and Pinot by 53 seconds.
Deceuninck Quick Step's Alaphilippe gained a total of nine bonus seconds and Pinot (Groupama-FDJ) picked up eight at the top of the final ascent and on the finish line.
Thomas is fifth, 1:12 off the pace with his Ineos team mate Egan Bernal a further four seconds adrift.
Vincenzo Nibali, the 2014 champion, dropped out of contention when he cracked on the Cote de la Jaillere and reached the line 4:25 off the pace.
Thomas was frustrated that Alaphilippe's move came shortly after he had made his way back into the peloton.
"I'm fine but it was just frustrating," he said. "It was a key moment in the race. (Michael) Woods crashed and took out Gianni (Moscon) and me and I just got tangled in Gianni's bike.
"By the time I got up to the group I was gassed for a bit and obviously that's when they started to sprint away. It's annoying and frustrating but to come back like I did is good.
"If I hadn't crashed I could have followed (Pinot and Alaphilippe) and it's a totally different story then. Still a lot of racing to go though."