The win was the Greek's third straight over a top 10 opponent after he dispatched Dominic Thiem and Novak Djokovic in the previous two rounds.
Greek tyro Stefanos Tsitsipas' dream run at the Rogers Cup continued on Friday as the teenager toppled defending champion Alexander Zverev 3-6, 7-6(11), 6-4 to reach the semi-finals in Toronto.
The win over world number three Zverev looked unlikely when the 19-year-old dropped the first set and fell behind 2-5 in the second.
But Tsitsipas managed to save two match points and shifted the momentum after edging Zverev in a marathon second-set tiebreak.
Extending the match paid off for Tsitsipas as Zverev made a number of uncharacteristic errors in a tight third set and he handed the world number 27 victory with a double fault on match point.
The win was the Greek's third straight over a top 10 opponent after he dispatched Dominic Thiem and Novak Djokovic in the previous two rounds.
"I'm confused now, is this real?" Tsitsipas said. "This shows that with dedication and work, dreams do come true."
Zverev, 21, was accused of poor sportsmanship after he failed to congratulate his opponent when speaking to reporters after the match.
"I don't think he played that well. I think the match was absolutely pathetic on all levels," the German said.
"I'm very honest with you guys. Today was an absolute pathetic match I don't even think he played well."
Next up for Tsitsipas is a showdown with big-serving South African Kevin Anderson, who thrashed Bulgarian Grigor Dimitrov 6-2, 6-2 earlier on Friday.
Fourth seed Anderson, runner-up at Wimbledon last month, was never broken and won 81 percent of his first serves.
Top seed Rafa Nadal came from behind to send hard-hitting Croatian Marin Cilic packing with a 2-6, 6-4, 6-4 win in their quarter-final match.
The world number one was far from his best but took advantage of 43 unforced errors by Cilic, who converted just three of his 14 break-point opportunities.
"It is a very important victory. The match became so difficult," Nadal said.
"It's a very good victory against a big opponent. It's confidence and another chance to play again tomorrow and that's great news. I'm excited about it."
Nadal will face Russian Karen Khachanov, who defeated Dutchman Robin Haase 6-3, 6-1 earlier in the day behind 11 aces in a match that lasted less than an hour.
Nadal has won all three of his prior meetings with Khachanov including a straight-sets win in the round of 16 at the Monte-Carlo Masters in April, a tournament the Spaniard went on to win.
Halep defeats Garcia to reach semi-finals in Montreal
Top seed Simona Halep sent Caroline Garcia packing for the second consecutive year at the Rogers Cup in Montreal on Friday with a 7-5, 6-1 win to set up a semi-final showdown with Ashleigh Barty on Saturday.
The French Open champion showed no signs of fatigue following her marathon three-set win over Anastasia Pavlyuchenkova on Wednesday, running down balls to extend points and wear down the slower Garcia.
After a shaky start Halep won three straight games to take the first set and dominated the second set behind pinpoint serving and stout defense.
Next up for Halep is Australian Barty, who strolled to a 6-3, 6-1 win over Kiki Bertens in their quarter-final match earlier in the day.
The 15th-seeded Barty won 80 percent of her first serve points and broke Bertens four times as she cruised to victory.
Saturday's semi-final will mark the first career meeting between Halep and Barty.
American Sloane Stephens faced little resistance in her 6-2, 6-2 win over Latvia's Anastasija Sevastova in a match that took a little over an hour to complete.
With the win Stephens advances to her second consecutive Rogers Cup semi-final after falling to Caroline Wozniacki last year.
The 25-year-old U.S. Open champion will look to add her second hard court title of the year after she won the Miami Open in March.
But to do so she will have to get past defending champion Elina Svitolina after she dispatched Elise Mertens 7-5, 6-3 on Friday.
The fifth-seeded Ukrainian fired five aces and won 71 percent of her first serve points to book her ticket to the semis.
