It was a shock win for Lotto-Soudal’s Australian rider who overcame being dropped before some brilliant teamwork from his teammates carried him to the front for the final sprint,
Bryan Coquard and David Ballerini were left in Ewan's dust finishing behind the Aussie in second and third.
Remco Evenepoel remains in the lead in the general classification after finishing comfortably in the peloton.
Although struggling through the hilly parcours, Ewan was helped by the fact there were no successful breakaways allowing him to rejoin the peloton after he was dropped only 8km from the finish.
His Lotto Soudal teammates Harry Sweeny, Philippe Gilbert and Jasper De Buyst led the peloton for much of the final four kilometres, with De Buyst guiding Ewan through the technical final kilometre.
It put Ewan in the perfect position to put the power down for the final spring, leaving Coquard in his wake as the Sydney product claimed an incredible victory.
“It was a pretty tough race all day,” Ewan said.
“They say this was the hardest stage of the Tour. So, I was not really expecting to be there in the final and got a little bit gapped on the last climb.
“My team did a great job, waiting for me, and bringing me back to the front of the bunch, and we still had Philippe (Gilbert) and Jasper (De Buyst).
“We heard on the radio that they (Deceuninck-QuickStep) were riding full gas (on the final climb), and I knew that they wouldn’t want me to get back on. But I kept fighting with my teammates and they did a superb job waiting for me and bringing me back, and then also doing the lead-out afterwards."
Ewan said the win demonstrated his improvement this season and development as a WorldTour rider.
“I’ve said all along this year that I’ve felt much stronger in general, and I think I showed that today. Maybe the old Caleb wouldn’t have got through that," he said.
“To be honest, at the start of the stage I told the team that I wanted to go as deep as possible for training. It was a pretty solid day all day, but I was still there at the end.
“I thought this was the hardest stage of the Tour, so I thought that the guys who don’t have a chance in the sprints would have their opportunity today and that they would race really aggressively. It was a super-high tempo all day, and I think maybe a lot of the guys didn’t really have the legs to get away in the end.”