A younger Shapovalov had been set to play a five-minute exhibition before Nadal's match, which was ultimately cancelled as another match had gone long.
At Montreal: Third round: Denis Shapovalov bt Rafael Nadal 3-6, 6-4, 7-6 (4); Roger Federer bt David Ferrer 4-6, 6-4, 6-2; Robin Haase bt Grigor Dimitrov 7-6 (3), 4-6, 6-1; Diego Schwartzman bt Jared Donaldson 0-6, 7-5, 7-5.
In a glimpse of the future, 20-year-old Zverev - a four-time victor on the ATP Tour this season - needed three match points to see off Shapovalov and earn a showdown with Roger Federer in a repeat of the Halle decider, which the latter won in straight sets. Zverev advances to face the second-seeded and World No. 3 Roger Feder on Sunday.
He broke service for a 2-1 lead in the third Friday only to hand it back in the next game, but a roar went up when Mannarino wasted a chance to put away a game point and Shapovalov jumped on the chance to break for a 5-4 lead.
In Toronto, World No. 1 Pliskova advanced to the quarterfinals of the WTA Toronto hardcourt tournament while a pair of high seeds Venus Williams and Angelique Kerber crashed out in straight sets.
"I'm looking forward to a tough match because he can serve very well and he mixes up his tactics a lot", Federer said. "I believe it's because I was more aggressive coming to the net".
Shapovalov's win came less than 24 hours after a historic upset of first seeded Rafael Nadal.
Federer secured the decisive first break at 4-4 in the opening set, then got the better of three consecutive breaks early in the second.
"I was little bit bummed out because I thought Rafa was going to watch me play, you know, before his match", he said, laughing and eliciting chuckles from the reporters in the room.
"I didn't, but I managed to win because I kept fighting".