Sagan used his head and shoulder to shove the Jumbo-Visma sprinter as he came from behind, eventually forcing his way through to overtake Van Aert.
But the commissaires didn’t take kindly to the incident and relegated Sagan to last place in the peloton, which moved Sam Bennett (Deceuninck – Quick-Step) up to second and put Van Aert on the podium in third.
Speaking after the stage Van Aert, winner of two sprint stages in this year’s Tour already, said: “My opinion is I sprinted in a completely straight line at the right on the barriers.
“He just tried to create space for himself and for me you’re not allowed to do that.
“It’s already dangerous enough. I was really surprised and shocked at that moment, I felt something I was at maximum effort so I was really scared.”
Sagan’s relegation means Sam Bennett extends his lead in the points classification and the Slovakian may struggle to find enough opportunities to close the gap by the time the race reaches Paris.
At the line Van Aert made a gesture towards Sagan to show his frustration and he said he also had some bad language for the former world champion.
But when he then tried to approach Sagan again to explain why he was unhappy, Van Aert said he was only met with more bad language in return.
He said: “In the first moment I was so shocked and surprised that I was angry and I used some not very nice words to him. Afterwards I tried to explain it wasn’t right and I didn’t like what he did,but the only thing that came back was other strong words, so it was hard to have a conversation.”
Van Aert isn’t convinced that he would have won the stage if Sagan hadn’t shoved him, but said it was “frustrating” to end like that.
He added: “I’m also a good bike handler but it doesn’t come into my mind to create space like this.
“There wasn’t a gap.”