Ewan was the first to finish the 194.3km stage from Balıkesir to Bursa in an uphill sprint to claim his first podium of the Tour.
Juan Jose Lobato (Nippo Vini Fantini Faizane) came in second and BORA-hansgrohe's Sam Bennett finished third after nearly five and a half hours of racing.
“Already after the first stages, although not having the best legs, I knew that a stage win would be possible, so I got more confidence as the race progressed and also my legs were feeling better as well," Ewan said.
"The last three to four kilometres uphill were harder than I first thought. I did some research online beforehand, but you can never really see the gradients that way.
"The team always kept me in a perfect position during the run-up to the finishing climb, so I didn’t have to fight too much before the roads started to rise. That way, I could save some valuable energy before the final kick up to the line, which clearly helped me at the end.
"Sam Bennett would have been hard to beat, but when he was supposed to start his sprint, I noticed that he was pretty tired. That is when I made my move.
"I was lucky that I still had a good acceleration left in the end, with Lobato starting his sprint quite early. I did not produce my best sprint power ever but it seemed like I still had the most energy left.”
Bennett continues to lead the general classification with a 24sec advantage over team-mate Felix Grobschartner and another two seconds ahead of Jhonatan Restrepo (Manzana Postobón).
“I really didn’t know what to expect today, a lot of guys were ready for a sprint and it was a tough finale at the end," Bennett said.
"I knew Caleb was sitting on my wheel, but I was already on the limit. I wanted him to go first but when he moved, I was on a big gear and struggled to follow him.
"Anyway, I think Caleb was the fastest today and I say congrats. It was pretty cold today, maybe that affected me a little, but I will try again to win another stage here in Turkey.”
The longest stage of the Tour of Turkey unfolded as expected with five riders on the early attack, but the task was almost impossible for the break with its progress blunted by a solid head wind. Eventually, all were swept up by the peloton some 10km from the finish.
Stage 5 from Bursa to Kartepe features a 1,300-meter climb which is set to decide the race.