TORONTO — Alexander Zverev called it an absolutely pathetic match. Stefanos Tsitsipas can call it another big upset victory.
Tsitsipas saved two match points before clinching the quarterfinal win on a double-fault as he stunned the second seed and defending Rogers Cup champion 3-6, 7-6 (11), 6-4 on Friday afternoon.
"I kind of fooled him when I was on the court," Tsitsipas said. "I did some things that he didn't expect me to do."
The Greek teenager — who has surged to No. 27 in the world rankings from No. 168 a year ago — reached his first career semifinal at an ATP World Tour Masters 1000 event.
Tsitsipas, who beat seventh-seeded Dominic Thiem and ninth-seeded Novak Djokovic earlier in the week, became the youngest player to beat three top-10 players at one tournament since Rafael Nadal — who was also 19 — did it at Monte Carlo in 2006.
Tsitsipas will face fourth-seeded Kevin Anderson of South Africa in Saturday's semifinals at Aviva Centre. Anderson posted a 6-2, 6-2 victory over fifth-seeded Grigor Dimitrov of Bulgaria in the early match.
On Friday evening, Robin Haase of the Netherlands was to play Russia's Karen Khachanov and Nadal, the No. 1 seed from Spain, was to meet sixth-seeded Marin Cilic of Croatia.
Tsitsipas started with a bang on a warm, sunny afternoon on centre court, reeling off eight straight points for a quick 2-0 lead. Zverev answered by winning the next four games before taking the set in a tidy 32 minutes.
The 21-year-old German moved ahead early in the second set but Tsitsipas broke at 3-5 and held serve to pull event.
"He started putting some balls into the court," Zverev said. "I think before he was playing really bad. And I actually thought I was playing bad the whole match. So I lost a little bit of concentration.
"I lost a little bit of rhythm, but it wasn't — I mean even if I would have won, it wasn't a good match."
In the tiebreaker, Zverev won a 20-shot rally to get his first match point at 6-5 but Tsitsipas poured on the pressure from the baseline and tied it. Tsitsipas saved another match point before converting his fifth set point at 13-11 when Zverev sprayed a return wide.
"I always say when the opponent played better, I'm probably one of the most honest guys on tour," Zverev said. "Today was an absolutely pathetic match. I don't think he played well."
Both players secured early breaks in the deciding set and Tsitsipas — who had started to mix up his shots more often and change service speeds — saved three break points to pull ahead 5-4.
At 30-40, Zverev floated his second serve well long to end the match in two hours 27 minutes.
"To be honest, we played three sets and all three sets should have been three, three and three," Zverev said. "If we would have played best-of-five, that's what the score should have been. But as I said, I didn't feel the ball at all. I didn't play well."
Tsitsipas struggled with a first-serve percentage of 47 per cent, well below Zverev at 70 per cent. But the teenager converted all four of his break-point opportunities while Zverev was five for 14.
"The level of tennis today, in my opinion, was not the highest — it was alright," Tsitsipas said. "People seemed to love it, loved the show and everything. I would say I played OK."
Tsitsipas, who lost in straight sets to the German in their first career meeting last week in Washington, will move into the top 20 when the new rankings are released next week.
In the doubles quarterfinals, the top-seeded duo of Austria's Oliver Marach and Croatia's Mate Pavic edged Jean-Julien Rojer of the Netherlands and Romania's Horia Tecau 6-7 (5), 7-5, 10-6.
Raven Klaasen of South Africa and Michael Venus of New Zealand beat Americans Mike Bryan and Jack Sock 7-6 (5), 6-4 while Croatia's Nikola Mektic and Austria's Alexander Peya defeated Anderson and Djokovic 7-5, 7-5.
Americans Sam Querrey and Rajeev Ram were to face second-seeded Henri Kontinen of Finland and Australian John Peers in the late doubles match.
Play continues through Sunday at the US$5.94-million tournament on the York University campus. Zverev beat Roger Federer in last year's singles final at Montreal.
Follow @GregoryStrongCP on Twitter.