The US Open is turning into WWE where there’s plenty of action even after the match is over.

A new wave of post-match drama ensued around midnight when Stefanos Tsitsipas criticized Daniel Altmaier for utilizing an underhand serve after being defeated by him in the second round of the U.S. Open.

“Next time, don’t wonder why I hit you, OK? No, I’m just saying if you serve underarm,” remarked Tsitsipas as the pair exchanged handshakes, a moment caught by a hot mic.

The Greek athlete then added, “If you serve underarm,” to which Altmaier seemed to reply, saying “too late” while giving Tsitsipas a pat on the shoulder, trying to put some space between them.

Tsitsipas again said, “If you serve underarm” to his German foe, walking toward him after Altmaier had already started to move away.

Altmaier had enough at this point, hand waving him before going to shake hands with the umpires.

Boos began raining down at this point, but they changed to cheers after Altmaier raised his hands triumphantly while he walked back onto the court.

“You knew that was going to happen,” the television broadcaster said. “There was going to be something between these two…”

Tsitsipas’ point of contention is that Altmaier used an underhand serve a few times, which Reuters describes as a “legal but rarely used underarm serve.”

His line to Altmaier about wondering why he hit him indicated that he may have tried to peg him with the ball during the match, according to The Guardian.

Altmaier used the controversial underhand tactic as part of a rally to win in five sets, 7-6(5), 1-6, 4-6, 6-3, 7-5, in a match that lasted four hours and 26 minutes in Flushing Meadows, per Reuters.

The World No. 56, said he does not enjoy such post-match interactions, with Jelena Otapensko giving Taylor Townsend an earful earlier in the tournament in a similar situation.

“I know that sometimes in the heat of the moment you can say stuff which you don’t normally would like to say,” Altmaier said, per Bounces. “You regret afterwards. So I think that we all know the discussions at the nets, I’m not a fan of it.

“Even if I would have lost, I would not enter discussions because it’s just like heat of the moment. You need to cool down. Let’s see if he reacts to it or he sticks to his opinion. Which is, for me, it’s fine. Like, I think I know what I did and that’s it. It’s part of the game.”

Altmaier’s win put him in the third round of this tournament for the first time in his career, and he will face eighth-seeded Alex de Minaur on Saturday.

“It’s difficult to describe right away how you feel,” Altmaier said on the court after the win. “A big relief, honestly. … I left my heart out here and I hope you enjoyed it.”