Slovenia's Primoz Roglic once more prevailed on his toughest test yet to remain on course for Tour de France glory, while Miguel Angel Lopez soloed to a breathtaking stage win atop the highest mountain of the race.
With the Slovenian pair Roglic and Tadej Pogacar playing cat and mouse for the overall leader's yellow jersey, the cagey Lopez grabbed Wednesday's 17th stage by the throat with a surging burst for the line that also allowed Roglic to leave behind his 21-year-old rival.
Lopez's win at high altitude gave Colombia something to celebrate on the day 2019 champion Egan Bernal pulled out after he and his team Ineos failed to live up to expectations.
With two massive mountains the queen stage ascended to 2,304m altitude atop the Col de la Loze, where Tour rookie Pogacar lost just a handful of seconds to Roglic in their ongoing war of attrition.
Pogacar has however been racing virtually alone, and won plaudits challenging Roglic, who has appeared rock-steady with a powerful climb posse surrounding him in Jumbo's black and yellow outfits.
The Slovenians have been the story of the Tour and will likely square off for the overall win on stage 20's mouthwatering individual time trial.
As Lopez pulled away team Jumbo leader Roglic also showed too much power for Pogacar on the last agonising kilometre.
"That was hell," said the former ski jumper Roglic.
"I'm glad this is behind me," he added, merely needing to survive without a major incident to win this year's Tour.
"Every metre counts on a climb like that."
Shorn of Bernal Ineos co-captain Richard Carapaz produced a doomed solo bid as the Giro champion was caught on the ever-changing gradient of the final 7km above 2,000m as the top 10 experienced a slight shake-up.
A day after the race was cleared of Covid-19 to run all the way to Paris on Sunday, French President Emmanuel Macron was present as the peloton struggled through villages full of ubiquitous baskets of flowers hanging from Swiss-style ski chalets.
In the rarefied air that suits the men from the Andes, the 26-year-old Lopez leapfrogged compatriot Rigoberto Uran and extended his lead over Adam Yates and Richie Porte.
Roglic now leads his young compatriot Pogacar by 57 seconds with just three real races left before the Tour gets to Paris.
Suffering from a bad back for a month now Bernal, his Tour defence in tatters, said a sad goodbye to the 2020 edition when Ineos decided to protect the long-term interests of their 23-year-old captain by withdrawing him.
But his compatriot Astana captain Lopez, who is known as "Superman" in his homeland after fighting off three thieves who tried to steal his bike, gave Colombia something to shout about.
Lopez had complained earlier in the race that Jumbo's dominance was suffocating the race, but saw his opportunity on a mentally challenging finale where the varying gradient called for constant adaptations.
"I felt strong coming into the race and on the Grand Colombier, which was the first big one (climb) of the race, like the ones I train on in Colombia, I felt good," Lopez said.
"I won many things in my life, but this is impressive and I worked so hard to get here," said the man who has previously finished on the podium at both the Giro and the Vuelta.
The long hard 14km struggle up the Col de la Madeleine to its 2,000m summit was at the halfway point of the race.
Lopez made the difference on the even higher Meribel mountain with a sudden turn of pace while Roglic and Pogacar were watching each other.
"I felt at home over 2,000m, as I live at 2,500m above sea level," he explained. "But I won't win, the others ahead of me are too good on time trials. I'm just going to enjoy myself."
The key remaining challenge is stage 20, the 36km individual time trial that runs over 30km of rolling terrain before tough 6km ascent up the fabled Planche des Belles Filles on Saturday.
The final day on Sunday is a kind of parade, except for the concluding eight laps of the Champs-Elysees, where Ireland's Sam Bennett will face a stern challenge for the green sprint jersey from seven-time winner Peter Sagan on a last-gasp dash for the line.
Overall standings after stage 17 of the Tour de France, from Grenoble to Col de la Loze on Wednesday:
1. Primoz Roglic (SLO/Jumbo) 74hr 56min 04sec, 2. Tadej Pogacar (SLO/UAE) at 57sec, 3. Miguel Angel Lopez (COL/AST) 1min 26sec, 4. Richie Porte (AUS/TRE) 3:05, 5. Adam Yates (GBR/MIT) 3:14, 6. Rigoberto Uran (COL/EF1) 3:24, 7. Mikel Landa (ESP/BAH) 3:27, 8. Enric Mas (ESP/MOV) 4:18, 9. Tom Dumoulin (NED/JUM) 7:23, 10. Alejandro Valverde (ESP/MOV) 9:31, 11. Guillaume Martin (FRA/COF) 10:35, 12. Damiano Caruso (ITA/BAH) 12:30, 13. Richard Carapaz (ECU/INE) 19:55, 14. Warren Barguil (FRA/ARK) 25:22, 15. Nairo Quintana (COL/ARK) 30:51, 16. Sepp Kuss (USA/JUM) 35:53, 17. Peio Bilbao (ESP/BAH) 53:24, 18. Pierre Rolland (FRA/VCC) 55:11, 19. Carlos Verona (ESP/MOV) 1hr 08:42, 20. Gorka Izagirre (ESP/AST) 1.10:18.
Green points jersey:
1. Sam Bennett (IRL/DEC) 278 pts, 2. Peter Sagan (SVK/BOR) 231, 3. Matteo Trentin (ITA/CCC) 218, 4. Bryan Coquard (FRA/VCC) 171, 5. Caleb Ewan (AUS/LOT) 158, 6. Julian Alaphilippe (FRA/DEC) 150, 7. Wout van Aert (BEL/JUM) 131, 8. Michael Morkov (DEN/DEC) 120, 9. Tadej Pogacar (SLO/UAE) 112, 10. Alexander Kristoff (NOR/UAE) 100
Polka-dot king of the mountains jersey:
1. Tadej Pogacar (SLO/UAE) 66 pts, 2. Primoz Roglic (SLO/JUM) 63, 3. Miguel Angel Lopez (COL/AST) 51, 4. Benoit Cosnefroy (FRA/ALM) 36, 5. Pierre Rolland (FRA/VCC) 36, 6. Nans Peters (FRA/ALM) 32, 7. Richard Carapaz (ECU/INE) 32, 8. Marc Hirschi (SUI/SUN) 31, 9. Richie Porte (AUS/TRE) 28, 10. Lennard Kamna (GER/BOR) 27
Under-25 white jersey:
1. Tadej Pogacar (SLO/UAE) 74hr 57 min 01sec, 2. Enric Mas (ESP/MOV) at 3:21. 3. Valentin Madouas (FRA/FDJ) 1hr 24min 17sec, 4. Daniel Martinez (COL/EF1) 1.48:51, 5. Lennard Kamna (GER/BOR) 1.52:47, 6. Harold Tejada (COL/AST) 2.11:39, 7. Neilson Powless (USA/EF1) 2.27:20, 8. Niklas Eg (DEN/TRE) 2.30:43, 9. Marc Hirschi (SUI/SUN) 2.42:49, 10. Pavel Sivakov (RUS/INE) 3.36:45.