Demare, who had been accused by Germany’s Andre Greipel of holding on to a car to make it through the mountains on Stage 16, silenced his critics with a superb sprint finish to claim the win on Thursday.
“The best answer I could give Andre Greipel was to win today,” the Frenchman was quoted following his victory.
“Obviously what he said hurt me, and was also insulting. It’s regrettable that people doubt my performances.
“I know I’m not the best in the mountains, but I work hard to make sure I get through them.”
Yellow jersey holder Thomas, of Team Sky, finished 31st and remains 1min 59sec ahead of the Netherland’s Tom Dumoulin while his team-mate Chris Froome remains in the third position.
“I think we’re expecting the worst, hoping for the best,” Thomas said.
“I think guys will try to take any opportunity they can. It will be interesting, but we’ve been riding really well all race.”
There was another crash on Thursday with Colombia’s Nairo Quintana and Britain’s Adam Yates among the several riders who were caught.
Slovakia’s Peter Sagan had been the victim of a huge crash himself on Wednesday and the sprint king wants to just get over the finish line after suffering some big injuries.
“I can’t complain, I could be worse,” Sagan stated after the completion of Stage 18.
“After what happened yesterday with the crash, I was in a lot of pain today. I think tomorrow will be much harder, but I consider myself lucky that, after such a crash, I’m still in the race and not sitting at home.
“But it was my own mistake yesterday. There was no motorbike in front of me. I flew into the forest, like a bird.”
The 200.5km long 19th stage of the iconic race is set to get underway on Friday with the final stage set to take in Paris on July 29.
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.”