A largely flat 171 kilometre stage 18 from Trie-sur-Baïse to Pau was expected to provide relief to riders after a short but steep route yesterday.

A five man breakaway were allowed to go clear for the majority of the stage, but they were caught with around 15km to go.

It set up for a sprint finish that Slovakia’s world champion Peter Sagan would have previously been favourite for, but a crash yesterday raised uncertainty over whether he would pursue a fourth stage win of the race.

Demare would ultimately emerge as the fastest rider on the day, as the Frenchman came through to triumph in 3 hours, 46min, 50sec.

Second place finisher Christophe Laporte complained his fellow French rider had obstructed his sprint, but the result stood.

Norway's Alexander Kristoff and Edvald Boasson Hagen rounded off the top four, with Sagan ending eighth.

"I didn't fight in the mountains for nothing," said Demare.

"It's a fantastic reward.

"In every difficult moment, I only believed in winning a stage. 

"It might sound strange after the hard time I had uphill yesterday, but I've got good legs.

"Several sprinters aren't here anymore but I never gave up, I kept faith in my ability to win a stage."

The result was added reward for Demare after he struggled through the climbs, while his success came after German rival Andre Greipel, who abandoned on stage 12, implied Demare had received illegal help from the team car yesterday to stay within the time limit.

Greipel would later issue an apology after Demare stated he would provide data from his ride yesterday.

The stage had no impact on the general classification with the main contenders finishing together.

Britain's Geraint Thomas still enjoys a 1min 59sec buffer over The Netherlands' Tom Dumoulin.

Thomas' Team Sky team-mate Chris Froome, the four-time and reigning winner of the race, lies 2:31 down in third.

The final mountain stage will take place tomorrow in Laruns.

The penultimate stage will be a 31km individual time trial in Espelette, before the ceremonial final stage in Paris on Sunday (July 29).