Team Sky leader looks set to win the 2017 race as Romain Bardet struggles to make enough inroads on Froome's lead.
Tour de France: Froome retains yellow as Team UAE's Atapuma claims second to Barguil on Stage 18
Tour de France leader Chris Froome remained rock-solid on a thrilling Col d'Izoard climb on Thursday and now looks unstoppable in his bid for a fourth title in Paris.
Fans wedged onto the 2,360m sun-bleached summit roared home Warren Barguil as the Frenchman broke clear to win the stage, but it was not the story most of the home fans wanted.
They had arrived hoping to see Romain Bardet make a decisive attack on the seemingly unflappable Froome and snatch the yellow jersey on the last day in the Alps.
The AG2R La Mondiale rider did beat Team Sky's Froome over the line at the end of the 179km stage which culminated in a brutal 14km ascent of Izoard - hosting a summit finish for the first time in Tour history.
But his third place, behind Sunweb's Barguil and Colombian Darwin Atapuma, only allowed him to shave four seconds off Froome's lead as the British rider finished just behind him in fourth place with Rigoberto Uran fifth.
One-time race leader Fabio Aru's hopes disintegrated as he suffered in the stunning Alpine scenery and slipped from fourth to fifth in the overall leaderboard behind Froome's teammate Mikel Landa, who looks capable of a podium finish in Paris.
"I gave it my all," said Bardet, who looks like finishing second behind Froome as he did last year. "I risked everything. I have nothing to regret. Now we have the time trial but the Tour is already a success."
Everything that happened during the ride from Briancon, including the category one Col de Vars, was a prelude to the eagerly anticipated final act on Izoard - a climb that is part of the folklore of the Tour, up there with Mont Ventoux.
A large breakaway group of some 54 riders had gradually splintered by the time the stage leaders reached the start of the Izoard climb.
Kazakh Alexey Lutsenko was the first man to attack before he was overtaken by Team UAE's Darwin Atapuma with 6km remaining.
But it was to be Barguil's day as he sewed up the polka dot jersey. He timed his move to perfection and with 1.5km to go he burst past Atapuma and powered to victory.
Back down the road Bardet, whose AG2R team had tried valiantly to wear down the Team Sky train from halfway up the Col de Vars, finally attacked Froome on the lunar landscape of Izoard. But he could make no impression.
It was Froome who separated himself from his rivals with a devastating burst of speed that looked terminal for Bardet and Uran before they hauled themselves back to the man in yellow.
Bardet crossed before Froome for a small time bonus but remains 23 seconds behind with Uran at 29.
Only an extraordinary meltdown or a crash seem likely to stop the Briton taking a fourth Tour title as Friday's 222km-stage towards the Mediterranean is relatively simple and Saturday's is a time trial in Marseille in which Froome will be confident of extending his advantage.