Roglič was the main aggressor of the top favourites, attacking a number of times on the final ascent of the stage, the Col d'Aubisque. He was brought back mostly through the efforts of Dumoulin (Team Sunweb) who was defending his second overall position from the Slovenian in fourth.
Despite not being able to get a gap on the Aubisque uphill, Roglič continued to attack on the descent into Laurens, eventually obtaining a gap that he was able to extend all the way into the finish, winning the stage by 19 seconds.
At the end of the stage, Dumoulin claimed that Roglič had been aided by the presence of a motorbike on the final descent.
"He was flying downhill," said Dumoulin, "and eventually I got dropped on a straight part just because he was on his tube and full in the slipstream of the motorbike.
"I was sprinting to his wheel and I couldn't get any closer. I just got dropped on the only straight part of the downhill. It's ridiculous really."
Pacing by motorbikes is a contentious issue within cycling, with Dan Martin (UAE Team Emirates) claiming earlier in the race that the peloton chasing him had been the beneficiaries of a motorbike, which had helped the main bunch bring him back after an attack on Stage 15.
Motorbikes aren't controlled by any partisan interests, normally they are driven by Tour de France staff and are ferrying photographers and TV cameras and so rarely attract time penalties for drafting. Many riders take the opportunity to draft motorbikes if they are there, many consider it the responsibility of the motorbike to not be in a position that can be taken advantage of.
Drafting off team cars is a different matter, a rule that Dumoulin himself fell foul of in Stage 6, where he was penalised 20 seconds for sitting behind his team car.
With the stage win, Roglič moved up to third overall, ahead of Chris Froome (Team Sky) and potentially within striking distance of Dumoulin in second if the big Dutchman has a bad day.
"I am super disappointed," said Dumoulin. "It doesn't make sense. That bike should have been behind us."
Race leader Geraint Thomas (Team Sky) was a bit more diplomatic than Dumoulin.
"The way he did get the gap was a little surprising," said Thomas."I was concentrating on the corners, following Tom's (Dumoulin's) wheel. There has been an issue with motorbikes getting too close, but I didn't see it."
"Roglic was better, that is not up for discussion. He couldn't do anything about it, he was the strongest and claimed a nice victory."
Roglič himself wasn't forthcoming on the issue, with the former ski-jumper neither confirming nor denying the influence of a motorbike.
"What can I say? I can't comment on things on which I don't have influence over," said Roglič . "I don't see where the problem is."
