As they had done on previous stages, Ag2r had attempted to apply more pressure on Froome and Sky for their GC hope, Romain Bardet. But Sky once again proved to be the stronger team, safely delivering Froome to the line with no significant time lost to Bardet, or any of his other rivals.
The stage honours atop the Col d'Izoard went to Warren Barguil (Team Sunweb), who took his second stage victory of the 2017 race and secured his position in the polka-dot jersey of King of the Mountains. Darwin Atapuma (UAE) survived from the day's large escape group to claim second, with Bardet in third and Froome fourth.
Froome now leads Bardet by 23 seconds overall, with Uran slipping from second to third at 29 seconds – still a very tightly-packed top three after nearly three weeks of racing.
Fabio Aru (Astana) saw his hopes of a podium place fade further, as he lost touch with the Froome group on the Izoard to lose just over a minute. The Italian is now in fifth overall as Froome's team-mate Mikel Landa elevates to fourth.
The stage represented the final real chance for the climbers to attempt to overhaul Froome before Saturday's decisive time trial – the British rider's favoured discipline. However, they all failed to do so and now the question will be how much time Froome can gain in the test against the clock in Marseille. Froome would surely love to seal a fourth Tour win with a stage victory, something that has eluded him so far.
The Big Break
The final mountain stage of the 2017 Tour de France was always likely to attract a large number of riders to get themselves in an escape group – but few would have predicted that number to be 54.
The vast break contained no rider within 30 minutes of Froome overall, so they were allowed plenty of leeway from the Sky-led bunch. By the mid-way point of the stage, after the category three climb of Côte des Demoiselles Coiffées, the gap was pushed out to over eight minutes.
Breakaway specialist Thomas De Gendt (Lotto-Soudal) did more than his share of pace-making at the front of the break going into the intermediate sprint at Les Thuiles, 88km from the finish, won by Sonny Colbrelli (Bahrain-Merida).
On to the category one Col de Vars, the break split in two, with a lead group of 22 and a chase group of 32. Behind those two groups, the peloton was strung out in the tailwind with Bora-Hansgrohe assisting Sky in pacing the peloton.
Why Bora? The reason seemed opaque with no rider in the top 10 overall, although they had missed putting a rider in the escape. Either way, it meant that Sky could save the legs of Luke Rowe and Christian Knees for longer than originally expected.
Romain Sicard (Direct Energie), Darwin Atapuma (UAE), Tony Gallopin (Lotto-Soudal) and Alexey Lutsenko (Astana) broke free of the shattering escape group towards the top of the Col de Vars, with Lutsenko cresting the summit first.
There was a change in the order of the peloton as they tackled the final kilometres of the Col de Vars, with Bardet's Ag2r setting a fierce speed to put Sky and Froome under pressure. However, Froome looked relaxed, and at one point grabbed a mussette and passed them around his team-mates.
There were no attacks over the top of the Vars from the yellow jersey group, as they hit the descent together, Ag2r/Bardet still leading Sky/Froome.
At the front of the race, Lutsenko, Sicard, Atapuma and Gallopin were joined by six more riders as they headed towards the ascent of the Col d'Izoard, with five and a half minutes over the Froome group with 25km remaining. Lutsenko was on his own again as the final climb commenced but was chased down and passed by Atapuma.
Back in the peloton, Ag2r continued to set the pace ahead of Sky onto the Col d'Izoard but were burning through their riders one by one and with 6km to go only Bardet was left as Sky resumed control with Michael Kwiatkowski, Mikel Landa and Mikel Nieve sat in front of the yellow jersey.
Barguil attacked from the Froome group on the climb, followed briefly by Alberto Contador (Trek-Segafredo), and he quickly built up a gap. Next to attack from that group was Dan Martin (Quick-Step Floors), and although Sky caught up with him it put Fabio Aru (Astana) into trouble.
As Kwaitkowski swung off, Landa attacked off the front – a clever Sky move to put Froome's rivals under pressure and be forced to chase. Landa started the day in fifth overall, just 1-24 behind Froome, and could easily move up the GC.
With 3km to go, Bardet launched an attack, with only Froome and Uran able to follow. Only 200 metres later, Froome accelerated away from Bardet and Uran to reach Landa. It was Uran who put in the effort to chase, with Bardet on his wheel.
At the same time, Barguil caught and then passed Atapuma to go solo at the front of the race – but now with only 25 seconds on Froome, Landa, Bardet and Uran into the final kilometre.
As Barguil celebrated his win over the line, Bardet tried to shake off Froome and Uran but could not unhitch the yellow jersey. Nonetheless, his third spot behind Barguil and Atapuma means his bonus seconds secured him second place overall ahead of Uran.
Aru was visibly struggling, and finished 1-02 behind Froome and Bardet. In the fight for the best young rider's jersey, Simon Yates (Orica-Scott) lost 22 seconds to rival Louis Meintjes (UAE) as they finished ninth and seventh respectively. And Irishman Martin rode well again to finish eighth.
The 2017 Tour de France continues on Friday with stage 19, starting in Embrun and finishing in Salon-de-Provence, 222.5km later. Along the way there are three category three climbs with a final descent off the Col du Pointu and into a relatively flat run-in to the finish.
With much still at stake in the Tour, it is hard to predict how the racing will pan out: the stage winner could easily come from a break, a bunch sprint or perhaps a group of GC contenders.
Many of the GC riders will undoubtedly be mindful of the following day's individual time trial in Marseille, before the race concludes with its traditional finale in Paris on Sunday, July 23.
Tour de France 2017, stage 18: Briançon to Izoard, 179.5km
1. Warren Barguil (Fra) Team Sunweb, in 4-40-33
2. Darwin Atapuma (Col) UAE Team Emirates, at 20 secs
3. Romain Bardet (Fra) Ag2r-La Mondiale
4. Chris Froome (GBr) Team Sky, at same time
5. Rigoberto Uran (Col) Cannondale-Drapac, at 22 secs
6. Mikel Landa (Esp) Team Sky, at 32 secs
7. Louis Meintjes (RSA) UAE Team Emirates, at 37 secs
8. Daniel Martin (Irl) Quick-Step Floors, at 39 secs
9. Simon Yates (GBr) Orica-Scott, at 59 secs
10. Alberto Contador (Esp) Trek-Segafredo, at 1-09
General classification after stage 18
1. Chris Froome (GBr) Team Sky, in 78-08-19
2. Romain Bardet (Fra) Ag2r La Mondiale, at 23 secs
3. Rigoberto Uran (Col) Cannondale-Drapac, at 29 secs
4. Mikel Landa (Esp) Team Sky, at 1-36
5. Fabio Aru (Ita) Astana, at 1-55
6. Daniel Martin (Irl) Quick-Step Floors, at 2-56
7. Simon Yates (GBr) Orica-Scott, at 4-46
8. Louis Meintjes (RSA) UAE Team Emirates, at 6-52
9. Warren Barguil (Fra) Team Sunweb, at 8-22
10. Alberto Contador (Esp) Trek-Segafredo, at 8-34
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