It was supposed to be the hors d’oeuvre, a gentle palate opener of a stage before the meatier main dishes in the Pyrenees later in the week. Instead the 218km journey from Carcassone to Bagnères-de-Luchon turned into a chaotic, sprawling and utterly unpredictable mess. Yet despite all the drama Team Sky’s Geraint Thomas crossed the line serene and in control. Crucially his 1min 39sec lead over Chris Froome remains intact and from now on he can count the stages remaining until the finish in Paris on one hand.

Thomas has held the yellow jersey for a week without any visible signs of strain or weakness. But he will be grateful to have survived an extraordinary day that took a sharp pivot after 30km when French farmers interrupted the race by rolling giant haystacks across the road to protest against new French labour laws and a lack of investment in the region.

Police deterred the protesters by blasting them with pepper spray, but the cloud lingered and, as the peloton approached, many riders sustained burning eyes and lungs, prompting pandemonium as the race was stopped for 15 minutes. Those affected included Thomas, who vigorously pawed his eyes, and Peter Sagan in the green jersey, who drowned his face with water.

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Dan Martin, who sits 10th in the general classification, was more bemused by the experience. “What was it, mace?” he asked. “That’s a new experience. I’m always open to new experiences, but pepper spray during the race – you could feel it in the lungs there for a bit. It wasn’t exactly pleasant. But they dealt with it pretty well, and the medical team gave the guys who needed it some attention. Bizarre, though.”

Later there were two high-speed crashes. One left Philippe Gilbert in a ravine and the other appeared to rob Britain’s Adam Yates of his chance of a stage win. “I’ve never seen anything quite like it,” admitted Froome. He was far from the only one.

“I understand the right of people to protest, but we have to let the riders race,” said the race director, Christian Prudhomme. “They have a difficult enough job as it is. Respect all the riders – French, foreign, the yellow jersey, all the riders.”

After the restart the riders split into two large groups, with the GC riders content to sit back and let a bunch of 47 riders extend their lead to over eight minutes by the time they reached the first of the day’s three significant climbs, the second-category Col de Portet-d’Aspet.

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At this point Quick-Step’s Gilbert attacked and established a minute or so lead at the front. But then on the descent he suddenly lost control of his bike and ended up being catapulted over a wall and plunging into a ravine. Amazingly, after being checked by doctors, the Belgian gave the TV cameras the thumbs up as he set off again. He somehow finished the stage too, despite a broken kneecap, although he later abandoned.

The Quick-Step directeur sportif, Brian Holm, admitted he feared the crash had resulted in far more serious consequences. “You look down and see holy fuck, he was pretty far down,” he said. “There were some rocks — it wasn’t like a soft forest he landed on. But as soon as I saw him, he was swearing. That was a good sign. You knew he was in one piece.”

Gradually the pack was whittled down until Yates attacked with four kilometres to the summit to the Col du Portillon remaining. At the top he led by just over 20 seconds. Yet as the Frenchman Julian Alaphilippe started to gain Yates crashed on the slippery descent into Bagnères-de-Luchon and lost of a lot of skin and an even greater amount of time.

While Alaphilippe, who won stage 10 last week and also holds the polka dot jersey, sprinted away with the stage Yates was tentative and could finish only third after being overtaken 3km out by the Spaniard Gorka Izagirre. “It’s one of them things,” said Yates. “I’ve took more risks on more technical descents in the past and never had a problem. We recon all these stages but you never know what’s coming up. It was a bit damp.” When asked whether he had any bad injuries, he shook his head. “Just bad morale – because we’ve been working for a while to win one of these stages.”

Next the riders face Wednesday’s 65km stage to Saint-Lary-Soulan. It is a dynamite stick of a day, short but explosive and with the potential for untold damage – particularly during the unrelenting climb to the summit up to the Col de Portet, the highest finish in the race. It also averages nearly 9% gradient during its 16km length.

“It’s going to be massively decisive,” said Thomas. “The final climb is possibly the toughest climb of the Tour. Anything can happen. But it’s a big, big day and for sure there are going to be some splits.”

Thomas will be acutely aware that Yates’s brother, Simon, led the Giro d’Italia for 13 days, only to lose 38 minutes on the Colle delle Finestre three days before the finish. It was Froome who applied the savage strike, breaking away from the peloton and racing solo to victory. Could history be about to repeat itself?