Chris Froome (right) riding ahead of Nairo Quintana, yesterday.

Britain’s Chris Froome took another big step towards a third Tour de France title when he dropped his main rivals in the finale of the 17th stage, a 184-km mountain trek won by Russian Ilnur Zakarin yesterday.

Froome (Team Sky) attacked inside the final two kilometres in the last ascent, a punishing 10.4km climb at an average gradient of 8.4 per cent and Dutchman Bauke Mollema, second overall, as well as last year’s runner-up Nairo Quintana, could not follow.

The Briton finished on the wheel of former team-mate Richie Porte (BMC), the Australian emerging as a potential podium finisher in Paris.

Froome extended his lead over Mollema to 2:27 and compatriot Adam Yates to 2:53.

Colombian Quintana (Movistar), who has been lacking his usual stamina in the long climbs, is fourth, 3:27 off the pace after losing 28 seconds to Froome when he was expected to attack.

The decisive move was made by Porte, who jumped away from the favourites’ group 2kms from the line, with Froome the only rider able to follow him thanks to a short but brutal acceleration.

Porte climbed from seventh to sixth overall, 4:27 off the pace, but his recent form suggests he will continue to move up the general classification, taking sole leadership at BMC after team-mate Tejay van Garderen cracked in the penultimate climb of a gruelling day in the Swiss Alps.

Romain Bardet continued his fine Tour, moving up one spot to fifth at 4:15 ahead of today’s 18th stage, a brutal 17-km uphill time trial from Sallanches to Megeve.

A 14-man breakaway, featuring world champion Peter Sagan and his Tinkoff team-mate Rafal Majka, the polka dot jersey wearer, took shape after a crazy first hour of racing during which the peloton covered 51.8km.

Then, Majka and Colombian Jarlinson Pantano (IAM Cycling), winner of the 15th stage, attacked the leading group in the descent.

They were joined in the final climb by Zakarin (Katusha), who jumped away 6.5km from the finish, followed by Pantano.

The Russian went again with 5.8km left and never looked back, his medallion tapping on his bare chest until he managed to zip up his jersey before crossing the line, his face a mask of pain, for a first Tour stage win.