Egan Bernal had the edge over the other top Tour de France contenders as France’s Julian Alaphilippe hung on for dear life to retain the yellow jersey at the end of a punishing day in the Alps on Thursday.

Nairo Quintana won the 18th stage, a 208-km trek at high altitude from Embrun, but all eyes were on the battle for the title, as his fellow Colombian Bernal powered away from a reduced pack about two kilometres from the top of the Col du Galibier with his rivals unable to respond.

His advantage quickly rose to 43 seconds, but an attack from his Ineos team mate, Geraint Thomas, dented his lead while Frenchman Thibaut Pinot then reined in the defending champion with most of the other favourites on his wheel.

Only Alaphilippe was dropped, but the world number one made his way back to the group in the high-speed descent to the finish.

He leads Bernal by 1:30 going into the last two competitive stages in the mountains and while his yellow jersey seems to be hanging by a thread, Alaphilippe has shown he will not go down without a fight. Thomas is third and 1:35 off the pace with Dutchman Steven Kruijswijk in fourth place a further 12 seconds behind. Pinot is in fifth position, 1:50 adrift of Alaphilippe.

Thomas’s move, however, highlighted a leadership conundrum at Ineos as the defending champion effectively chased down his team mate and brought his rivals closer.

“The call was made for Egan to go and hopefully that would kick it off a bit, but it didn’t really - (Alaphilippe’s team mate) Mas just started riding his tempo,” said Thomas.

“That’s when I went as well, just to test. But at least Egan gained some time on everyone else.”

Bernal, who is now best-placed to deprive France of a first home-grown Tour winner since Bernard Hinault’s triumph in 1985, said he had spoken to Thomas before his attack.

“G asked me how I was feeling. I said I was feeling really good so he asked me to attack to try to move the race,” he said. Pinot, who was the in-form rider in the Pyrenees, could not follow Bernal, but found the strength to catch Thomas at the end of the 23-km climb up the Galibier, which stands 2,642 metres above sea level.

“I wasn’t on a great day,” said Pinot.

“The goal was to follow the best. I couldn’t do it with Bernal, he was too strong today. Thomas also made a strong attack that hurt us but we managed to come back.”

Reuters