The Welshman sat in sixth position in the general classification, less than a minute off Alejandro Valverde in fourth place, and well on course for a top-10 overall finish.
Then he was hit by a rolling cannonball in the shape of Giant-Alpecin’s Warren Barguil, knocking Thomas off the side of the road and down into a ravine.
The crash looked horrific – viewers were worried that the Team Sky man may not get out of the ravine in one piece, such was the speed of the crash and the force of the collision with a telegraph pole.
After the camera panned away to Thomas’s teammate Chris Froome, it returned to show pictures of Thomas not only alive and well, but back on his bike and powering down the last few kilometres of the descent.
In all, Thomas lost only 40 seconds to his rivals in the incident, quite remarkable when you consider the severity of the incident.
The following two days saw Thomas move up to fourth overall – thanks in part to Tejay van Garderen’s abandonment – but on stage 19 the mountains got the better of him, seeing him slip down to 15th place, where he remained until Paris.