Shapovalov becomes the youngest quarter-finalist at an ATP World Tour Masters 1000 tournament. He's also the second-youngest player to beat Nadal (Coric, 2014 Basel).
"It's so tough. A lot of the times he just hits a shot that's way too good. I was managing to get a lot back when I could. But, you know, he's honestly the best player I've ever played in my life," Shapovalov said.
"You could tell why he's won so many Grand Slams. His ball was just so heavy. He's such a warrior out there. So it's honestly, like a dream come true for me to beat a player like that."
For the Spaniard, a return to No. 1 in the Emirates ATP Rankings will have to wait. Nadal would have returned to No. 1 for the first time since June 2014 if he had reached the semi-finals in Montreal.
Andy Murray will remain at No. 1 for another week but at the Western amp; Southern Open in Cincinnati next week, Nadal and Roger Federer will battle for the top spot.