He's the youngest player to beat three top-10 players in one tournament since Rafael Nadal - who also was 19 - in 2006 at Monte Carlo. Milos Raonic of Canada was scheduled to follow Djokovic's win on center court, but that match was delayed by rain.
"I tried few things that I didn't try before, and I played a little bit more with variety and changed the pace a bit of the ball, played deeper, played smarter".
"I always say when the opponent played better, I'm probably one of the most honest guys on tour", Zverev said. He earned his first match point with a cross-court forehand victor and clinched his two-hour, 18-minute victory with another one, dropping his racquet to the court with joy. "I knew I was playing pretty good today".
Top seed Rafa Nadal battled past Swiss wild card Stan Wawrinka 7-5, 7-6 (7-4) and will next meet Marin Cilic, who took down Argentinian Diego Schwartzman 6-3, 6-2.
At 30-40, Zverev floated his second serve well long to end the match in two hours 27 minutes.
"The Canadian teenagers are great players", the former world No. 1 said.
"I thought it went really well out there", said Polansky, who's never made it past the second round of a Rogers Cup.
Bulgarian fifth seed Grigor Dimitrov laboured for nearly two and a half hours to subdue Frances Tiafoe of the United States 7-6 (7/1), 3-6, 7-6 (7/4).
Tsitsipas let a double-break point opportunity slip at 4-4 in the second set, eventually giving up the game after back-to-back shanks. "People seemed to love it, loved the show and everything".
His trademark retrieving skills were on display throughout the match but Tsitsipas used strong groundstrokes to push the pace and force Djokovic to fully stretch on several rallies. (The early break in the third set) was everything.
Play continues through Sunday at the US$5.94-million tournament on the York University campus.
In other results, fourth seed and Wimbledon runner-up Kevin Anderson downed Ilya Ivashka of Belarus in straight sets. He rose to prominence past year with a stellar run at the Rogers Cup in Montreal that ended with a semifinal loss to eventual champion Alex Zverev.