Froome suffered a mechanical problem on the Mont du Chat, the last of three hors categorie climbs on the day, and as the three-time Tour victor was calling for the team auto Aru attacked in a clear breach of cycling's protocol.
He careered across the road and clattered into Ireland's Dan Martin, bringing the two crashing into the rocky side of the road in the final 25km of the 181.5km stage from Nantua to Chambery.
A stricken Porte was treated by doctors before being carried into an ambulance and taken to hospital, while Martin picked himself up and finished the stage despite going down for a second time. I've just seen the images of Richie Porte's crash and that leaves you with a frightful feeling.
Thomas started the day 12 seconds adrift of Team Sky team-mate Froome in second spot in the GC standings, but his race was ended when he damaged his shoulder in a fall.
It was the fourth time already in just over a week that Thomas had crashed during this Tour.
Five riders in total crashed out of the race on Sunday while two-time former victor Alberto Contador was able to carry on quickly after coming down on an uphill section.
However, Porte's BMC sporting director Fabio Baldato insisted the team had come prepared, particularly for the Mont du Chat climb and descent. "Job done!" Like Quintana he came home 1min 15sec behind Uran and now sits sixth at 1:44, with Quintana remaining eighth but now out to 2:13 behind Froome. "I want to thank the other riders, who did not attack".