In a quarterfinal match against Alexander Zverev at the Shanghai Masters, Federer hit a return volley into the net and was clearly frustrated. Medvedev, whose run was described by 20-time Grand Slam champion Roger Federer as "crazy", won 84 per cent and 67 per cent of his first and second serve points respectively while Tsitsipas won 82 and 44 per cent.
Friday marked another point of evidence toward the arrival of the next generation of stars, including 22-year-old Alexander Zverev and 21-year-old Stafanos Tsitsipas.
Federer produced his best tennis at 40-0 down, rescuing himself from the brink with a series of inspired shots to force a tie-break in which he survived two more match points before levelling things up.
"Being in a massive final here in Shanghai is very special for me because it's my first final in China, in general". Federer had been 5-0.
Tsitsipas smacked the ball out of the court in a rage before Medvedev sealed the match in the 12th game of the second set.
Federer clearly had no intention of discussing the incident after the match, abruptly dismissing a question from a reporter about why he was unhappy with the umpire's decision during the post-match press conference.
"So you could write on Twitter, you mean?"
He clung fiercely to that advantage against an uncharacteristically irritable Federer, who was docked a point in game four after striking a ball away in anger, having already been warned for doing so earlier.
"He's different this year", Zverev said.
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Zverev said the victory over Federer had given him a major confidence boost.
"The young guys are knocking on the door big time, it's exciting, it's great", he said.
"To be honest, I really felt good today and I felt like I could win this match".
Zverev beat Andrey Rublev of Russian Federation 6-0, 7-6 (4) in the last match of the night.
It was a double celebration for Tsitsipas, who also confirmed his place in the prestigious season-ending ATP Finals.
When this is added to the two titles he has won this year - in Budapest and Stuttgart - and his final appearance in Munich, it all adds up to a good year for the 23 year old from Rome.
Zverev is now through to his first semi-final Masters of the year, where he will play Italian Matteo Berrettini.
The Russian has prevailed in 28 of his past 31 matches and is now on an eight-match winning streak, all of which have come in straight sets. The only time he lost a hard-court match after winning the first set was against Gael Monfils in Rotterdam.
Nobody should be writing the triumvirate off: the 32-year-old Djokovic is number one and the player poised to take top spot off him in the coming weeks is the 33-year-old Nadal. It just went step by step.
"When I was serving for the match he changed it again, surprised me again", Medvedev said.