The Welshman was firmly in contention as the peloton prepared to begin the 13.6km climb to the summit but saw his hopes dashed when a rider in front of him clipped a parked police motorcycle and brought Thomas and several others down.
Thomas, leading Sky's pink jersey bid with Spanish teammate Mikel Landa, bravely got back on his bike to complete the stage but crossed the line five minutes behind stage winner and new race leader Nairo Quintana of Movistar. He added: "We were all racing, then someone in front of me hits a motorbike. My shoulder popped out. "I felt good but then I crashed, and my race was over." It is not the first time in recent years riders have suffered directly as a result of incidents with motorbikes involved in the race.
Copyright Agence France-Presse, 2017