Chris Froome works with Bardet, but is surprised to see Aru dropped in the Tour de France

Chris Froome (Team Sky) imagined that he would end the day in the Serre-Chevalier Alpine Ski resort with three rather than two rivals breathing down his neck as he fights for a fourth Tour de France title.

Italian Fabio Aru (Astana), however, has slipped behind in the race's general classification. Instead of the top four separated by 29 seconds after stage 17 over the Galibier, three are within 27 seconds. Froome, as always, remains in charge.

"The big surprise today was Fabio Aru, who lost a bit of time," Froome said. "I expected him to go on the attack, but yeah it is always the third week of a Grand Tour that tests everyone and here there is no hiding if you are having a bad day in the third week."

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Froome sat in his yellow jersey with the press, digesting the 183-kilometre stage. It traversed several cols, including the Galibier at 2,642 metres.

"I think the altitude affected everyone. It was over 2,500 metres of climbing today and it was a very hard day of climbing. My legs felt a lot better today than they did a week ago in the Pyrenees."

Last week at the Peyragudes airstrip in the Pyrenees, Froome's chances of winning a fourth Tour title appeared to be slipping away. Now, in the Alps, the odds are tipping in the favour of the 32-year-old Kenya-born Brit.

Froome followed the attacks from Frenchman Romain Bardet (Ag2r La Mondiale) and kept him and Colombian Rigoberto Urán (Cannondale-Drapac) under control. Their group distanced Aru by the top of the Galibier and worked in unison to drill their lead deeper.

Primoz Roglic (LottoNL-Jumbo) won the stage with a solo move. Urán took second place and the six-second bonus, Froome finished third with the four-second bonus.

"I just needed to do enough today to stay up front. I didn't need to do anything crazy given I have a lead on the on the GC guys and given tomorrow will be a big summit finish to the Izoard," Froome added.

"I'd heard about the situation of the race, [Bardet with 10 kilometres remaining] was telling me that Aru had been distanced and it was a good opportunity for us to collaborate and work together, which I had no problems with."

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Instead of a four-horse race, Froome heads a three-horse race with both Urán and Bardet locked at 27 seconds behind.

"I wouldn't quite say that,” he said, “even Alberto Contador's attack today put us under a lot of pressure and the team had to respond."

Froome faces the final of three summit finishes in this Tour tomorrow, the Col d'Izoard.

"Tomorrow will be all about the legs and who has the legs after a really tough stage today. It's depends on a lot of things, what the other riders do and how the legs are," Froome continued.

"This is not a massive margin compared to other years, but a margin I have nonetheless. I'm pretty happy with it. If I went into the time trial with the same margin, 27 seconds, I would be pretty confident."