Julian Alaphilippe kept the Tour de France lead on Thursday as Colombians dominated the Alpine ascents with Nairo Quintana storming to the stage victory and Egan Bernal climbing from fifth to second overall.

Bernal, at 22 the youngest man in the race, sprung his attack three kilometres from the summit of the Col du Galibier, running the gauntlet of the fans packed onto the final stages of the relentless 23-kilometre climb, which ended at over 2,600m.

Bernal is perfectly primed in second place at 1min 30sec from Alaphilippe, who clung once more to his lead, with Welshman Geraint Thomas, the defending champion, a further five seconds back in third, Steven Kruijswijk in fourth at 1min 47 and Thibaut Pinot fifth at 1min 50sec.

For 17 stages, Bernal had been kept largely under wraps by Ineos, but as the race approached the sort of altitude where he grew up, he finally unfurled his wings in the rarefied oxygen, scampering off to put 31 seconds into his four closest rivals.

Bernal is causing a stir in Colombia.

"I'm here, second, and maybe I can win the Tour, but it's going to be really very hard to achieve that, for now I'm second," said a serene looking Bernal.

"There are five other guys still in there," he said, refusing to brag.

For the 29-year-old Quintana the stage win saved his Tour de France.

The Movistar captain blew his lines in the Pyrenees, but gained almost six minutes on the main contenders to finish the first full day in the Alps seventh overall.

'I'm still in yellow' 

Alaphilippe seems unconquerable. After he was dropped on the climb, the Frenchman galvanised himself, limiting his losses before the crest, and then catching all his rivals, except Bernal, with a virtuoso descent, frequently adopting his 'supertuck' aerodynamic downhill crouch to stunning effect.

Alaphilippe looked like a man on fire after the race.

"They all wanted to attack me and that's what they did," he said laughing.

"Look, I'm still in yellow," he said pointing to the overall leader's jersey he will don for a 14th time on Friday.

"When Bernal attacked I just hung on however I could and then let it rip on the descent."

"I took a lot of risks and really took great pleasure in that fight back," said Alaphilippe.

The other fancied Frenchman Pinot said after the race it had been a bad day for him.

"We couldn't follow Bernal and you have to be able to keep up with the best. Thomas also launched a big attack and we got him back so I suppose it was not so bad in the end," said the emotional Pinot.

It was also a day of redemption, of sorts, for French climber Romain Bardet, who had dropped to more than 25 minutes off the overall pace.

After embarking from Embrun in searing heat which reached 40 degrees Celsius (104 Fahrenheit), he Quintana and Adam Yates, who have all had poorer than expected Tours, joined a mass breakaway.

Even though he was dropped by Quintana in the battle for the stage win, Bardet claimed the polka dot 'King of the mountains' jersey as well as his smile, after spending two weeks looking like a broken man. He was also runner up on the day.

Friday's stage from Saint-Jean-de-Maurienne to Tignes also features two dreadful mountain climbs with the first one topping out at 2,800 metres while the race ends with a summit finish at the Alpine ski resort.

There will be no descent at Tignes for Alaphilippe to catch up if he gets dropped again and when reminded of this fact the man who has worn the yellow jersey with style and bravery answered simply, "I know" and smiled again.