However, the commissaries retrospectively handed Dumoulin his 20 second time penalty pushing him further down the standings.
It was Martin's second Tour stage win after his first in 2013.
Dumoulin, the time trial world champion and 2017 Giro d'Italia victor, was slowed by a tire puncture at the foot of the final ascent and lost 53 seconds.More news: Bentley Mulsanne WO Edition unveiled
"Then I had to chase and that effort was fatal". He was one of eight top Tour contenders to gain some handy time that may prove vital come the Tour finish in Paris on July 29.
"I saw the moment".
"So I set off, kept my head down, kept going and my legs felt good". "There are a lot of twists on the Tour and this time luck was not on our side".
"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.
There was a slight split in the peloton behind, with Mitchelton-Scott's Adam Yates part of a group that picked up a couple of seconds on the main pack, which contained Team Sky's Chris Froome and Geraint Thomas, Movistar's Nairo Quintana and Mikel Landa, and BMC's Richie Porte.More news: Thailand cave: Museum and movie in the works for Tham Luang
Martin was one of several team leaders along with former Tour victor Vincenzo Nibali and two-time runner-up Nairo Quintana who were caught off-guard by an attack by Quick-Step midway through the stage during a straightaway that was exposed to crosswinds.
A breakaway group of five riders - Laurent Pichon (Fortuneo-Samsic), Anthony Turgis (Cofidis), Dion Smith (Wanty-Groupe Gobert) and Damien Gaudin and Fabien Grellier (both Direct Energie) - hit the front from the off and built a gap of nearly seven minutes before it stabalised.
This was the first summit finish of this Tour.
Friday will see the riders take on the longest stage of the race at 218km when they take off from Fougeres and finish in Chartres.More news: Microsoft counters Slack with a free version of Teams
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