Egan Bernal is poised to become the first Colombian to win the Tour de France after finishing Saturday's penultimate stage in the yellow jersey.
Tradition dictates that the race leader is not challenged on Sunday's largely processional final stage to Paris.
Bernal, 22, will become the youngest Tour winner for 110 years, with Ineos team-mate Geraint Thomas in second.
Dutchman Steven Kruijswijk moved up to third as Julian Alaphilippe faded on an Alpine stage won by Vincenzo Nibali.
Italian Nibali, winner of the Tour de France in 2014, was in the day's break and attacked again on the climb to the finish at Val Thorens, winning by 10 seconds from Spain's Alejandro Valverde.
Bernal and Thomas, who won last year's Tour, finished stage 20 a few seconds later, crossing the line arm-in-arm, with huge grins on their faces. They came into the race as joint leaders for Ineos and, providing they both reach the finish in Paris on Sunday, will end it first and second in the general classification.
"We're now close to making it official," said Bernal. "There's one stage left but, normally, if everything goes well, I can say that I've won my first Tour.
"It's incredible. I just want to get to the finish line in Paris and after I'll be calmer.
"Colombia is on the verge of winning its first Tour, We already had won the Giro d'Italia and La Vuelta a Espana, but the Tour was missing and it's a great honour to think that I'm the one achieving this."
Welshman Thomas, who ended the stage trailing in the overall standings by one minute, 11 seconds, wrote on Twitter: "Congrats Egan Bernal. What a rider. The first of many."
Bernal, who will also collect the white jersey as the best young rider in the race, will put to an end a run of four successive British winners – Chris Froome winning three of his four titles from 2015 and Thomas triumphing last year.
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The green points jersey classification will be won for a record seventh time by Slovakian Peter Sagan, who pulled a wheelie as he rode over the finish line several minutes after the stage winner, while the polka dot King of the Mountains jersey will go to Frenchman Romain Bardet.
That will be some consolation for the French supporters who had been hoping to see a home victory for the first time since Bernhard Hinault won his record-equalling fifth Tour in 1985.
Alaphilippe, the world's number one-ranked male cyclist, had led the race for 14 days, and after holding the yellow jersey through the Pyrenees in week two also retained it after the first day in the Alps.
However, he finally cracked on Friday's storm-shortened 19th stage and he again fell away on Saturday's final climb of the three-week race. He is set to finish fifth overall.
France's other big hope, Thibaut Pinot, had also looked strong in the Pyrenees, but a freak injury, caused when his thigh hit his handlebar on stage 17, saw him eventually abandon the race from fifth place during stage 19.
How stage 20 unfolded
Saturday's stage was reduced by 71km to just 59.5km, with one major climb – the 19.9km ascent of the Cormet de Roselend – chopped from the race because a landslide, caused by stormy weather in the Alps, had blocked the road.
That left the riders facing an unusual race along a dual carriageway across the valley from Albertville to the bottom of the day's solitary 33km climb to the ski resort of Val Thorens.
More than 20 broke clear and opened a lead of around two minutes, 30 seconds as they reached the ascent but with the race for the overall title happening in the peloton behind them, their lead was gradually eroded.
The Jumbo-Visma team of Kruijswijk, who started the stage in fourth, 88 seconds adrift of Bernal, set a furious pace from the bottom of the ascent.
Kruijswijk started the day just 12 seconds behind third-placed Thomas and 40 behind Alaphilippe and his team's efforts were rewarded when Alaphilippe cracked with around 13km of the race remaining.
However, Kruijswijk was unable to break the Ineos riders with Thomas and Bernal content to sit and ride tempo all the way to the finish line,
Dutch rider Kruijswijk eventually finished eight seconds behind Thomas to cement third place overall, one minute, 31 seconds behind Bernal.
Why the Bernal win will not be a surprise
The climbing specialist, who was born on 13 January, 1997 in Colombia's capital city Bogota at an altitude of 2,600m, showed his potential at last year's Tour, when he rode as a domestique to Thomas and four-time champion Chris Froome.
After pacing Thomas to victory on Alpe d'Huez and ultimately the overall title, Froome said: "He's got an amazing engine. You only have to look at what he did on Alpe d'Huez, for a 21-year-old, that's amazing.
"There is a lot in Egan that reminds me of myself when I was younger. It's great having him on the team and he brings a lot of young, new energy to the group."
He joined Team Sky for the 2018 season, after winning the prestigious Tour de l'Avenir – a stage race for under-23 riders that has seen manyRead More – Source