Stefanos Tsitsipas saved two match points to beat defending champion Alexander Zverev 3-6, 7-6 (13/11), 6-4 and reach the semi-finals of the Toronto Masters on Friday.
The Greek teenager, who turns 20 on Sunday's final day, defeated his third straight top 10 opponent at the tournament after knocking out Dominic Thiem in the second round and 13-time major winner Novak Djokovic in the third.
Tsitsipas is the youngest player to post three top 10 wins at a single tournament since a 19-year-old Rafael Nadal at Monte Carlo in 2006.
He will next face Wimbledon runner-up Kevin Anderson, who beat Grigor Dimitrov 6-2, 6-2.
"I'm confused now, is this real?," 27th-ranked Tsitsipas said after completing his prestige hat-trick of upsets.
The Greek rallied from a set and 5-2 down to turn the tables on Zverev, who had been bidding for a fourth Masters 1000 title.
"He started putting some balls into the court. I lost a little bit of concentration, a little bit of rhythm," Zverev said. "Even if I would have won, it wasn't a good match."
Tsitsipas broke in the ninth game of the second on the way into a tiebreaker, where he calmly converted on his fifth set point after saving two match points for the second-seeded Zverev.
Tsitsipas then salvaged four break points for 2-1 in the third, he traded breaks with the German and saved another trio of break points for a 5-4 lead.
He completed the victory after nearly two and a half hours on Zverev's sixth double-fault.
"This shows that with dedication and work, dreams do come true," Tsitsipas said. "I can see that it's real -- it's happening.
"I don't know what happened (in the second set) I just broke him (for 4-5), All along I could feel the crowd support, I knew I was still in the match."
Anderson's sweep past reigning ATP World Tour Finals champion Dimitrov was a rematch of their 2014 quarter-final duel in Canada when Dimitrov claimed one of his six wins against the South African.
"It definitely was a great match today. I felt I played really well right from the beginning," Anderson said.
"Right from the first point till the last, I felt I was in a really good frame of mind, playing the kind of tennis that I knew I wanted to be playing and needed to be playing.
"Getting off the court pretty comfortably definitely is a really good feeling."
Anderson hadn't defeated the Bulgarian for six years but he was in command throughout on Friday to reach his second career Masters 1000 semi-final having also made the last-four on clay in Madrid in May.
The big South African rolled into the semis in just 66 minutes, breaking four times while managing only a modest 11 aces.
"There's not much to say, he came out, played his game and everything was going his way," Dimitrov said. "He did everything well -- simple as that.
"There was not much for me to do. I tried as hard as I can, but I couldn't get into a rally."
Dimitrov will now head for the Cincinnati Masters where he is the defending champion. Tsitsipas won his only previous match over Anderson, beating him on clay last May in Estoril.
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