Roger Federer was given a point penalty as he followed Novak Djokovic out of the Shanghai Masters quarterfinals in a bad-tempered defeat to Alexander Zverev on Friday.
The 22-year-old German won 6-3, 6-7 (7/9), 6-3 as the Swiss legend was penalised after twice hitting the ball out of the court in anger and arguing with the umpire.
The sixth-ranked Zverev faces Austria's Dominic Thiem or Matteo Berrettini of Italy in the semifinals on Saturday.
Former number one Federer evaded questions about the umpire afterwards, shrugging his shoulders and firing back at one reporter: "So you can write something on Twitter, yeah? "Next question."
The 20-time Grand Slam champion saved five match points to force a deciding set, but he then became engaged in a continual war of words with the chair umpire.
The 38-year-old's trademark cool evaded him as the new generation of men's tennis stars took centre stage in Shanghai.
His point deduction came at 3-0 and 30-15 down in the third set, as he threatened to unravel.
He said that he "played alright", but was effusive about the rise of Zverev, Daniil Medvedev and Stefanos Tsitsipas, all in the semifinals in Shanghai.
"The young guys are knocking on the door big time. It's exciting, it's great," he said.
Tsitsipas said that he scares the "Big Three" after the young Greek stunned world number one Djokovic in their quarterfinal.
The 21-year-old has now defeated Djokovic, Federer and Rafael Nadal this year to burnish his fast-growing reputation.
On Saturday, though, he faces the red-hot 23-year-old Medvedev, who he has never beaten.
Tsitsipas recovered from losing the opening three games in just seven minutes to shock the reigning champion Djokovic 3-6, 7-5, 6-3.
Calling it the best comeback of his nascent career, the seventh-ranked Tsitsipas said he had dreamt of beating the "Big Three".
But rather than being intimidated by them, Tsitsipas said: "I honestly feel like they are more threatened than I am and that makes me more relaxed on court.
"I know I just have to hang in there and be able to be more aggressive.
"Once you get aggressive and they see you going for it, I might even say they get scared."