Britain’s Chris Froome put the hammer down in his bid to retain the Tour de France title when he won the 18th stage, a 17-km mountain time trial, to extend his overall lead to almost four minutes yesterday.

The Team Sky rider, aiming to become the first to retain the title since Miguel Indurain in 1995, clocked a best time of 30 minutes 43 seconds on a course featuring the punishing Cote de Domancy, a 2.5-km climb at an average gradient of 9.4 per cent.

He beat time trial specialist Tom Dumoulin by 21 seconds and Italian Fabio Aru by 33 seconds.

“I really didn’t expect to beat Tom today, pacing was key. I started off steady and really controlled that first part then gave it everything I had,” said Froome.

Dutchman Bauke Mollema, who started the day 2:27 behind Froome in the general classification, lost 1:25 and trails the defending champion by a massive 3:52 going into two final stages in the Alps before Sunday’s parade to the Champs Elysees.

Froome’s compatriot Adam Yates is third, 4:16 off the pace.

Today’s 19th stage is a demanding 146-km mountain trek with an uphill finish at Saint-Gervais Mont Blanc.