Calmejane, who rides for the Direct-Energie team, shrugged off a bout of cramp towards the end of the stage to earn the biggest win of his career.

The 24-year-old crossed the line 37sec in front of Dutchman Robert Gesink, who had begun to close the gap as a result of Calmejane's injury issues late on.

The LottoNL-Jumbo rider finished ahead of Guillaume Martin, who came through in third place.

"It's huge," said Calmejane, whose previous best result at a Grand Tour came when he won a stage of last year's Vuelta a España.

"It was everything I was dreaming of.

"When I had cramp in the finale, I decided to drop a gear so I could pedal softer."

His win has also moved Calmejane into first place of the King of the Mountains standings, handing him the famous polka dot jersey.

Froome, the defending champion who came into the eighth stage as the overall classification leader, was able to retain his yellow jersey despite a mistake 45km from the finish.

The Kenyan-born Briton, along with fellow Team Sky competitor Geraint Thomas, went off road on a descent but managed to recover.

He now leads Thomas by 12sec on the overall classification standings, with Italian Fabio Aru a further two adrift in third.

Froome is predicting a "decisive" day tomorrow during the ninth stage, a 181.5km mountain route from Nantua to Chambéry.

"That was a tough day," he said.

"Especially with Sunday's decisive day to come.

"A lot of guys in the break were a threat in the general classification so we went with the plan of putting Sergio Henao, Christian Knees and Mikel Landa in the break but even though we had guys in there we couldn't give it any room.

"We are going to see aggressive racing and gaps are going to open up.

"The descent to the finish in Chambéry is difficult."