Geraint Thomas admitted he felt "weak" as his Tour de France hopes suffered a blow on the brutal slopes of the Tourmalet.
The defending champion lost contact with the main contenders for with one kilometre to go of Saturday's 117.5km stage 14 from Tarbes as Thibaut Pinot took victory and Julian Alaphilippe finished second to extend his lead in yellow.
Thomas crossed the line 36 seconds after Groupama-FDJ's Pinot as his deficit to Alaphilippe grew to two minutes two seconds.
"Not the best day," Thomas said. "I just didn't feel quite on it from the start. I was quite weak. At the end I knew I just had to pace it. I didn't really attempt to follow when they kicked.
"I just thought I should ride my own pace rather than follow them and blow up on the steepest bit at the end.
"It's disappointing. I just tried to limit the damage."
Asked if he was unwell, the Team Ineos rider said: "We will see the next few days. From the start I just didn't feel great. There's still a lot to come."
It was a dramatic finish to another stage which rewrote the general classification as contenders were dropped one by one on the Tourmalet, with Mitchelton-Scott's Adam Yates and UAE Team Emirates' Dan Martin seeing their overall hopes effectively ended.
Alaphilippe had already defied predictions to pull out time on Thomas in Friday's time trial, but that it was the defending champion that cracked before the Deceuninck-Quick Step rider on the Tour's first hors categorie climb was an even bigger surprise.
Most observers still expect Alaphilippe's remarkable run in yellow to end sooner or later, but Thomas' rivals will have been hugely encouraged by his struggles here.
Steven Kruijsiwjk's Jumbo-Visma team looked strong as he cut his deficit to Thomas to just 12 seconds, while Emmanuel Buchman and Pinot are now 70 seconds behind the Ineos man in fifth and sixth respectively.
One by one contenders fell away on the Tourmalet, with Yates, Martin, Rigoberto Uran, Richie Porte, Nairo Quintana and more all distanced. AG2R La Mondiale's Romain Bardet was the biggest loser as he gave up more than 20 minutes on a brutal day, while Martin conceded five minutes 35 seconds and Yates six minutes 42 seconds on the back of their disappointing time trial performances.
French fans could celebrate however, as Pinot collected the stage win and Alaphilippe finished six seconds later in yellow.
For Pinot, it was a third career Tour stage win, and a sweet moment after he lost time in the crosswinds on stage 10.
"When you're a climber all wins at the Tour de France are beautiful, but to win on a monument like this, that's what I love" the 29-year-old said.
"We were motivated...I was angry. We will continue to fight. The Tour isn't finished yet."