Groupama-FDJ’s Demare held off Christophe Laporte of Cofidis and Alexander Kristoff of UAE Team Emirates in a sprint finish to claim his second career Tour win and his first this year.
Team Sky’s Thomas crossed the line with the front group to ensure he holds on to his advantage of one minute and 59 seconds over Tom Dumoulin of Team Sunweb going into Friday’s mountain test in the Pyrenees.
Demare’s stage win came on the day that German sprinter Andre Greipel, already out of this year’s Tour, apologised to him on Twitter after suggesting in an earlier post that Demare had used illegitimate means in order to avoid missing the time cut when struggling on the Col du Portet on Wednesday.
Despite Greipel’s apology, Demare said he had used his comments as motivation.
“I can thank Greipel today,” he said. “I thought of him a lot.”
On Thursday morning, Greipel wrote: “My apology go out to @ArnaudDemare and @GroupamaFDJ as I have had not the right to make that tweet based on GPS time, which can be wrong, plus I got the incorrect times he lost on the last hill. I’m sorry. Lesson learned: don’t tweet about sth you are not part off.”
The first sprint stage since Friday was contested by a vastly depleted field of quick men following the exits of Mark Cavendish, Marcel Kittel, Greipel, Fernando Gaviria, Dylan Groenewegen and Michael Matthews at various points in the Tour so far.
World champion Peter Sagan was also not the factor he might usually be after suffering a nasty crash on Wednesday’s stage.
The Bora-Hansgrohe rider hobbled on to his bike in the morning but had put his team on the front in the final few kilometres before eventually finishing eighth.
Sagan needs simply to make it to Paris to secure his sixth career green jersey.
After the drama of the past two days in the mountains, this was a largely uneventful stage, no doubt welcome to those still with an eye on the fight for yellow.
Wednesday’s stage winner Nairo Quintana of Movistar was caught in a crash along with Mitchelton-Scott’s Adam Yates with 105km to go but they were soon back on their bikes.
It was a great day for the Team Sky rider, who extended his lead over his rivals as he powered away in the final few kilometers to claim third place to Saint-Lary-Soulan behind stage winner Nairo Quintana and runner-up Dan Martin.
But as the Welshman approached the mountaintop finish of the race a man reached out from behind the security barriers to try and grab him.
Thomas, 32, stayed on his bike to increase his overall lead, pushing teammate Chris Froome down into third place.
Thomas opened up a 1min 59sec to Dutch rival Tom Dumoulin (Sunweb), with four-time champion Froome at 2:31.
But Cardiff native admitted his bid could have been ended by an “idiot”.
Pictures on social media show a bearded man wearing an AG2R-La Mondiale shirt apparently reaching out to grab Thomas. But he said it felt more like a “hit”.
“I definitely felt it. It didn’t feel like a grab, but like a hit,” Thomas said prior to the start of Stage 18 from Trie-sur-Baise to Pau on Thursday.
“I was going quite fast past him and it certainly moved me off my line and it was a bit of a shock.
“I think (he was) a bit of an idiot.”
Thomas maintained the gap to Dumoulin on Thursday as he finished 31st on the stage, four places behind the Dutchman, but at the same time.
If he avoids disaster on the way to the Champs Elysees in Paris on Sunday, Thomas will make history as the first Welsh winner of the Tour.
“We are coming to race our bikes, that’s all we want to do. The whole peloton wants to do it safely. That’s a bit too much,” he added.
Sky sporting director Nicolas Portal, a former rider with the team, appealed to fans to use common sense.
“Just try to think about what you are doing,” Portal said. “Would you do that in the streets in a city? No.
“If he crashed, broke his collarbone, it would have been done and finished just because someone doesn’t like this guy.
“It’s been three weeks with things happening. It’s like we are almost used to it, and that’s bad.”
Chris Froome said a “misunderstanding” led to a police officer knocking him off his bike after Stage 17 of the Tour de France on Wednesday.
Pictures emerged after the stage of Froome – wearing a grey jacket over his race jersey – responding angrily after the police officer tried to grab him as he was rolling back from the summit finish on the Col du Portet in the direction of the Team Sky bus.
“I was the first rider to come down the descent and one of the gendarmes grabbed my arm as I was passing,” Froome said.
“Obviously he thought I was a spectator going down the race route or something so he grabbed me. I was going at some speed so I came obviously, but it was just a misunderstanding.”
With no space to park the team buses at the top of the summit finish, riders had to turn around at the finish and descend back down the way they had climbed in order to reach the buses midway down the mountain.
Having given a few interviews at the finish, Froome donned a large grey coat over his white Team Sky kit and was accompanied by his bodyguard.
Unfortunately, with some riders still climbing towards the finish, one police officer mistook Froome for a fan descending on his bike. The officer asked Froome to stop, which caused him and his bodyguard to crash.
Froome’s Sky team have accepted it was a mistake, but fans may be more cynical after the way he has been treated during the Tour.
Froome has also been spat at and shoved by angry spectators, while he had what appeared to be a clear liquid thrown over him during Stage 14 to Mende amid simmering resentment towards Sky’s domination of cycling’s showpiece event.