UTRECHT, Netherlands (AFP) - Australia's Rohan Dennis will wear the first yellow jersey of the 2015 Tour de France after winning the opening stage timetrial in Utrecht on Saturday.

In the midst of a heatwave, Dennis was the only rider to complete the 13.8km course in under 15 minutes and beat three-time world timetrial champion Tony Martin into second with four-time world champion Fabian Cancellara third.

In the race for the overall title, reigning champion Vincenzo Nibali stole a march on his main rivals amongst the fantastic four.

Nibali finished in 15min 39sec to beat Chris Froome by 7sec with Alberto Contador at 14sec and Nairo Quintana losing 18sec to the Italian.

At the head of the race, though, Dennis won his first major timetrial in a stunning time of 14min 56sec to beat Martin by 5sec and Cancellara by 6sec.

"I've broken a dry spell of wins and what a way to do it," said a delighted Dennis, 25, an Olympic silver medallist on the track three years ago in the team pursuit.

There was disappointment for the home fans in the Netherlands, though, as their great hope Tom Dumoulin could finish only fourth at 8sec.

It was another Dutchman, 2010 national champion Jos van Emden, who was actually quickest at the halfway point but faded to fifth at 15sec.

Dennis was only a second behind Van Emden at the 7.1km time check, with both Dumoulin and Cancellara just one more second further back, but the Aussie finished strongest of all.

"I left it all out there; I went off harder than what I thought I should have and I came back harder than what I thought I could," said Dennis, who also set a record average speed of 55.446kmh for a Tour timetrial, beating the 21-year-old mark set by Britain's Chris Boardman.