The UAE Team Emirates rider made his play for the victory one kilometre out from the top of the famed climb which ended the 181km route from Brest to Mûr de Bretagne. He finished ahead of a hard-charging Pierre LaTour (AG2R La Mondiale) and Alejandro Valverde (Movistar).
The Irishman finally managed to break through an invisible barrier to win a stage, he has placed second in each of his past five Grand Tours without a win before his triumph in Bretagne.
"This is such an amazing feeling for me after so many second places at the Tour since my last one victory in the Grande Boucle," said Martin. "I was really relaxed all day and I was really looking forward to having a crack. When we got closer to the finish I was a bit nervous because of the head wind and I didn’t think it was going to happen.
"Then the race went really hard during the first part of the climb and a lot of riders got dropped and at that point I noticed that I didn’t have any team mates left so I thought why not have a try – and I did. It was the same place that I tried to attack in 2015, but got boxed in.
Martin made the most of a flatter section of the climb to launch a big attack that immediately put daylight between him and a Richie Porte-led (BMC) peloton.
"It was a case of waiting for everybody to be in the red, because I know I can go further into the red. I put in an explosive attack that I didn’t know I still had, but there was no way I was letting anyone beat me to the line."
There was a bit of chopping and changing on the general classification with Greg van Avermaet (BMC) still leading but his team-mate Tejay van Garderen swapped places with the previously third-placed Geraint Thomas (Sky).
The major news came when two pre-race favourites, Tom Dumoulin (Team Sunweb) and Romain Bardet (AG2R La Mondiale), suffered late mechanicals and lost time on their rivals despite working hard to reduce the gap.
Laurent Pichon (Fortuneo-Samsic), Damien Gaudin and Fabien Grellier (Direct Energie), Anthony Turgis (Cofidis) and Dion Smith (Wanty-Groupe Gobert) launched the break of the day and crafted a lead of over seven minutes on the peloton.
Smith, who briefly held the Polka Dot jersey of the mountains classification, was determined to narrow the gap to the new leader in that category, Toms Skujiņš (Trek-Segafredo), and his efforts in the break saw him claw back some lost ground with wins in the first two categorised climbs.
As the break was chugging along the peloton came to a long windy stretch of road with no tree cover, a scenario too tempting for Quick-Step Floors to resist.
The team massed its riders at the front and stretched the peloton until it split into three main groups on the road. The effort saw some riders with general classification aspirations lose touch, with the biggest casualty Primoz Roglic (LottoNL-Jumbo) who then had to consume a lot of his team's resources to rejoin the main peloton with 75km to go.
Under pressure, the break finally succumbed with 16km to go on the first of two ascents of the Mûr-de-Bretagne, which was summited first by Polka Dot jersey holder Toms Skujiņš. Mitchelton-Scott's Jack Bauer sensed an opportunity and soloed away to a 30-second lead but he was eventually caught with four kilometres of road remaining.
The teams of the general classification contenders drove the race hard into the bottom of the climb before the fireworks on the final climb. Thomas, Porte and Adam Yates (Mitchelton-Scott) were all prominent on the final climb, with Porte in particular laying down the hurt with an extended spell driving the pace.
Martin jumped away with over a kilometre to go in the race and while an aggressive Pierre Latour tried to make up the gap, the Frenchman fell agonisingly short, just a second behind Martin while Valverde led the first group across three seconds in arrears.
Chris Froome, Egan Bernal (both Team Sky), Rigoberto Uran (EF Education First-Drapac) and Steven Kruisjwijk (Lotto NL-Jumbo) all lost small amounts of time on the finish line, while Bardet and Dumoulin were the big losers of the day.