The main group of contenders, happy to let a 23-person breakaway have fun ahead, rolled over 17 minutes later, with second-placed Roglic and Tadej Pogacar locked together to maintain the 40-second gap between them.
There was no change at the top of the general classification, Rigoberto Uran third ahead of his compatriot Miguel Angel Lopez fourth and Briton Adam Yates fifth, Wednesday’s stage from Grenoble to Col de la Loze above Méribel should prove to be more decisive. .
Last year’s winner Egan Bernal, having dropped out of competition when he was pulled away from the Grand Colombier on Sunday, was late again and returned home in the grupetto alongside the sprinters and other stragglers on the mountain, at least managing to smile and joke. like he did.
Ineos had instead put his hopes on a stage victory, with Andrey Amador and Pavel Sivakov joining Carapaz in a large group that had been cleared to go up the road.
This group split decisively on the climb up the Montée de Saint-Nizier-du-Moucherotte just over 20 km from the line, with Carapaz attacking first but Kamna able to follow and then accelerate on the valley road until the last ramp to the line.
Kamna, 24, clinched a stage victory at the Criterium du Dauphine last month before taking second place ahead of Dani Martinez in stage 13 of the Tour on Friday.
“I feel great,” Kamna said. “It’s an absolutely great day for me now. It was a fight from the start and I knew I had to make it on my own at the finish. When I saw Carapaz accelerate, I said to myself: ‘It’s time to go’ and I just went all the way.
“It’s a big, big, big relief for the team and for me. I almost can’t imagine it. The step I have taken this year is huge and I am so happy to win today. ”
Nicholas Roche, whose father Stephen took the yellow jersey at Villard-de-Lans in 1987, was also at the break and returned to eighth place on the stage.
“You start the stage with the dream of winning another stage of the Tour de France but you can’t be too greedy either, you face some of the best riders on the planet,” said the Irishman.
“Sometimes it works, sometimes not, but Lenny showed today that he is the strongest on the climb. We saw that he was already strong from the start of the Tour, so he’s a well-deserved winner. ”
Neither Sam Bennett nor Peter Sagan were involved in the early attacks, so Bennett remains 45 points ahead of the former world champion in the battle for the green, but Matteo Trentin won the intermediate sprint to collect 20 points and close. his own deficit to Bennett at 60.