Geraint Thomas saw his Tour de France hopes fade on the brutal slopes of the Tourmalet as he lost contact with the main favourites in the final kilometre before Thibaut Pinot took victory.
Julian Alaphilippe once again defied expectations to finish second in the yellow jersey while Welshman Thomas was distanced and finished 36 seconds after Pinot.
It was a dramatic finish to another stage which rewrote the general classification as contenders were dropped one-by-one on the Tourmalet, with Adam Yates and Dan Martin seeing their overall hopes effectively ended.
Asked if he was unwell, Thomas said: "We will see the next few days. From the start I just didn't feel great. There's still a lot to come.
The new general classification shows Deceuninck-Quick Step's Alaphilippe has extended his lead over second-placed Thomas to two minutes and two seconds, while Steven Kruijswijk moves into third place ahead of Egan Bernal.
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 him 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.
Kruijsiwjk is now only 12 seconds in arrears to Thomas after a big performance from his Jumbo-Visma team, while Emmanuel Buchman and Pinot are 70 seconds behind the Team Ineos man in fifth and sixth respectively.