Pau, France (AFP) – Frenchman Arnaud Demare silenced his critics with a superb sprint finish that grabbed him victory over compatriot Christophe Laporte in the 18th stage of the Tour de France on Thursday.

Britain's Geraint Thomas finished close behind to tighten his grip on the yellow jersey three days before the 21st and final stage in Paris.

The Welshman holds a 1min 59sec lead on Dutch rival Tom Dumoulin (Sunweb) with his Sky teammate and four-time champion Chris Froome in third at 2:31 heading into Friday's 19th stage.

"I think we're expecting the worst, hoping for the best," said Thomas, who is expecting attacks from his rivals on the final day in the mountains Friday.

Froome, notably, is expected to come under attack by Primoz Roglic as the Slovenian, in fourth 16secs behind him, targets a podium place in Paris.

Thomas added: "I think guys will try to take any opportunity they can. It will be interesting, but we've been riding really well all race."

What was the penultimate chance for a diminished sprint field to snatch some glory was not going to be missed by the fast men of the peloton.

And a day after Slovakian sprint king Peter Sagan suffered injuries in a crash that almost ended his campaign, Demare capitalised.

His Groupama team worked hard, first in easily chasing down an early five-man breakaway, and particularly in the final, technical kilometres of the stage to make sure Demare was primed for a final burst to the line.

But the Frenchman, who angered Laporte by veering from his line when he sprinted from just inside 200 metres, was also inspired by comments aimed at him by Germany's Andre Greipel.

Greipel, one of several sprinters to pull out in the Alps, while others, like Mark Cavendish and Marcel Kittel, missed the time cut, accused Demare of holding onto a car to make it through the mountains on stage 17.

"The best answer I could give Andre Greipel was to win today," said Demare, who faced similar accusations on his way to victory in Milan-San Remo in 2016.

"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."

Bora rider Sagan is mathematically assured of his sixth green jersey for the points competition but, having won three stages already, admitted he was lucky to still be in the race.

"I can't complain, I could be worse," said Sagan.

"I was in a lot of pain. 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."

Colombian Nairo Quintana (Movistar) and Briton Adam Yates were among several riders caught up in a crash Thursday, although both got back on their bikes to finish the stage.

"It was a stupid fall," said Quintana, who claimed an impressive solo win on the summit of the Col du Portet on Wednesday that took him to fifth overall at 3:30 behind Thomas.

"I hurt my ankle and my shoulder, but I hope it's nothing. Tomorrow we'll be ready for the stage."

The peloton will notably tackle the Col d'Aspin, the Col du Tourmalet and the Col d'Aubisque on a stage 19 which finishes with a 20km downhill run into Laruns.