Britain’s Geraint Thomas dropped to third overall at the Tour de France but remained 95 seconds behind leader Julian Alaphilippe after Nairo Quintana won a mountainous stage 18 to Valloire.
Colombian Quintana attacked from a leading bunch, 7km from the summit of the Galibier, for a fine solo victory.
Defending champion Thomas rode away from Alaphilippe on the final climb but the Frenchman caught up on the descent.
Thomas’ team-mate Egan Bernal is second after the Colombian attacked late on.
“We wanted a hard pace and unfortunately we ran out of guys,” said Welshman Thomas.
“The call was made for Egan [Bernal] to go and that kicked it off. I couldn’t do much then other than follow.
“I had a little dig just to see if anything was going to happen and the guys followed me over the top. It was a good day for Egan gaining some time.
“We knew it would be hard to drop Alaphilippe, but there are two more big days to come.”
The 208km race from Embrun took in three Alpine mountain passes of more than 2,000m each in altitude and most of the action came on the final one of those, the 23km ascent of the 2,642m Galibier.
Quintana, who started the day almost 10 minutes adrift of the overall race lead, sprinted away from a bunch that had gone clear early on in the stage. He reached the summit around 90 seconds ahead of France’s Romain Bardet, and he maintained that advantage on the 19km descent to the finish.
Team Ineos’ Bernal also attacked on the Galibier, riding clear of fellow general classification favourites, including Thomas, Alaphilippe, Thibaut Pinot and Steven Kruijswijk.
Bernal managed to keep clear on the descent to Valloire, picking up 32 seconds to move up to second overall, 90 seconds behind Alaphilippe and five ahead of Thomas to leave Ineos second and third overall.
Alaphilippe is bidding to become the first French winner of Le Tour since Bernard Hinault won the last of his joint record five titles in 1985. He took the race lead on stage three, lost it on stage six and reclaimed it on stage eight. Since then, he surprisingly won stage 13’s individual time trial and has repelled attacks in the mountains, where he was expected to falter.
Thursday’s stage, the first of three big days in the Alps, was expected to test the Deceuninck Quick-Step rider and although he clearly struggled towards the top of the Galibier, losing 20 seconds to his rivals, his superior descending speed allowed him to quickly catch up.
However, stages 19 and 20 are both summit finishes, with Friday’s stage also featuring the highest point in the race at 2,770m.
The rider leading at the end of stage 20 will win the Tour, with Sunday’s finale into Paris a largely processional ride with tradition dictating that the race leader is not challenged.
Britain’s Adam Yates, who was part of Wedenesday’s initial break, fell away 10km from the summit of the Galibier. In his BBC Sport stage-by-stage guide, the Mitchelton-Scott rider has picked Quintana as his rider to watch on Friday.
Stage 18 result:
1. Nairo Quintana (Col/Movistar) 5hrs 34mins 15secs
2. Romain Bardet (Fra/AG2R La Mondiale) 1mins 35secs
3. Alexey Lutsenko (Kaz/Astana) 2mins 28secs
4. Lennard Kamna (Ger/Sunweb) 2mins 58secs
5. Damiano Caruso (Ita/Bahrain-Merida) 3mins 00secs
6. Tiesj Benoot (Bel/Lotto-Soudal) 4mins 46secs
7. Michael Woods (Can/Education First) Same time
8. Egan Bernal (Col/Ineos)
9. Serge Pauwels (Bel/CCC)
10. Steven Kruijswijk (Ned/Jumbo-Visma) 5mins 18secs
General classification after stage 18:
1. Julian Alaphilippe (Fra/Deceuninck-Quick Step) 75hrs 18mins 49secs
2. Egan Bernal (Col/Ineos) 1mins 30secs
3. Geraint Thomas (GB/Ineos) 1mins 35secs
4. Steven Kruijswijk (Ned/Jumbo-Visma) 1mins 47secs
5. Thibaut Pinot (Fra/Groupama-FDJ) 1mins 50secs
6. Emanuel Buchmann (Ger/Bora-Hansgrohe) 2mins 14secs
7. Nairo Quintana (Col/Movistar) 3mins 54secs
8. Mikel Landa (Spa/Movistar) 4mins 54secs
9. Rigoberto Uran (Col/EF Education First) 5mins 33secs
10. Alejandro Valverde (Spa/Movistar) 5mins 58secs