Daniil Medvedev lost his temper with Australian Open opponent Maxime Cressy, embarking on a furious on-court rant about his rival's playing style.
The Russian is the bookies' favourite to win the Melbourne tournament in the absence of world-number one Novak Djokovic, and has gone well so far.
He had only dropped one set in his opening three matches, and only Nick Kyrgios had given him any real resistance in the first week of action Down Under.
That changed when he met Cressy in the fourth round on Monday, though, as he found it tough to get to grips with the American's playing style.
Cressy prefers a serve-and-volley game which has largely been phased out of the sport, and therefore it is not often that others come up against such a playing style on tour.
It caused world number two Medvedev problems throughout their match, even though the Russian went on to win in four sets.
But it was during that final set that Medvedev really let his frustrations get the better of him, as he could be heard ranting about his opponent on the court.
He had a 2-1 lead in terms of sets and the fourth was tied up at two games each, but all the Russian wanted to complain about was the "lucky" player at the other side of the net.
"It’s simply unbelievable how lucky he is getting. I’ve never seen anything like this in my whole life," the 2021 Australian Open finalist was heard shouting.
He added: "This is my unluckiest day ever," as Cressy continued to hit the lines of the court perfectly on big points to keep himself in the game.
Medvedev went on to win that set 7-5 to secure his progress into the last eight, and later admitted he was not proud of what he had said to his opponent.
"I'm okay with [serve-and-volley] but he really did it well," he told Eurosport after the match. "I don't see anybody on the tour who would love it and say 'come on, do it again'.
"To be honest, I agree it was a great match. During the match it got a little crazy, I think with myself.
"I tried to say something into the air... to get into his mind a little bit and maybe he'll start saying 'what the hell is Medvedev saying?' and maybe he will miss some shots.
"But, I mean, I'm not happy with what I said today, but the most important is that I continued fighting."
Medvedev will meet Canadian Felix Auger-Aliassime in the quarter-finals, with the ninth seed expected to provide the Russian's toughest test of the tournament yet.
