Mûr-de-Bretagne, France (AFP) – Ireland's Dan Martin capped a daring, late attack on the steep Mur de Bretagne climb to snatch victory on the sixth stage of the Tour de France on Thursday that saw several yellow jersey contenders lose precious seconds to key rivals.

Overnight leader Greg van Avermaet (BMC) finished just three seconds behind in the main peloton to retain the yellow jersey ahead of Friday's seventh stage.

Van Avermaet leads Britain's Geraint Thomas (Sky) by three seconds in the overall standings, with American Tejay van Garderen (BMC) and France's Julian Alaphilippe (Quick Step) at five and six seconds respectively.

In a frantic finale that saw Martin break free of the pack 1km from the finish line to finish ahead of AG2R's Pierre Latour, defending champion Chris Froome of Team Sky lost eight seconds to his key rivals.

But Froome was not alone.

AG2R's Romain Bardet cracked in the heat of the final ascent and lost 31secs, while fellow contender Tom Dumoulin (Sunweb), the 2017 Giro d'Italia champion, lost nearly a minute after suffering a mechanical problem.

Opportunity Knocks

Martin dedicated his win to his new team, who he joined from Quick Step after overtures from Sky and BMC in the close season.

"I came to this team to be the leader and the pressure at the beginning, of being the leader is why I didn't do so well in Spring," said Martin.

"But there's a great feeling in the bus now, laughing and joking and this win is for them, they really looked after me."

"It was an early break but it was my only opportunity for the stage win as I'd never have got it in a sprint," explained Martin.

"When you get an opportunity, if you think about it, it's gone. You just go.

"So I set off, kept my head down, kept going and my legs felt good."

Yellow jersey wearer Van Avermaet described the climax as "an awesome finish."

"It was a very fast ascent and I just held on really," said the Belgian, who finished alongside team leader Richie Porte at three seconds off the pace to pull on the jersey for a third day.

Movistar veteran Alejandro Valverde was fourth on Wednesday's stage and came third here in another good ride for the 39-year-old, who is now eighth overall at 51sec.

But it could have been a terrible day for the Spanish team.

A group of five riders broke early on the 181km run from Brest to Mur-de-Bretagne and when the Quick Step team of stage contender Julian Alaphilippe suddenly accelerated on a plain, the peloton split into three with 100km remaining.

Movistar's Nairo Quintana, already 2 minutes 10 seconds down, and his teammate Mikel Landa were caught in the second of three groups and had to work long and hard to get back in the lead pack.

But it was on the final climb that the action took flight.

England's Adam Yates and the Mitchelton Scott team were shaping up for an attack, only for Porte to beat them to it.

As the Australian started to put his foot down, Martin flew past everyone and swiftly opened up a gap with a full 500m to climb.

The 31-year-old held on with a fast-closing Latour on his tail to claim the win and avenge his defeat on the Mur de Bretagne three years ago when the Irishman was denied by AG2R's Alexis Vuillermoz.

Peter Sagan was also in the final mix, coming eighth and picking up more points in the green jersey race and extending his lead on Colombian sprinter Fernando Gaviria.