(Video) Stefanos Tsitsipas Exchanges Heated Words With Daniel Altmaier on Underarm Serve After Losing to him at the US Open
Stefanos Tsitsipas will end the season with just two Grand Slam match wins this season following his loss to Daniel Altmaier.

Stefanos Tsitsipas and Daniel Altmaier exchanged heated words (X/welovetennis/The Tennis Letter)
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Stefanos Tsitsipas had some words with his second-round opponent, Daniel Altmaier, during their routine post-match handshake at the net. The former World No.3 was visibly frustrated at his opponent’s use of the underarm serve as he failed to win a match point during their tense five-set battle at the US Open.
Altmaier took the lead in the first set after a couple of brilliant volleys in the tiebreak. But Tsitsipas responded immediately in the second set, winning six of the seven games. He continued with the momentum in the third set, breaking the German once to win 6-4, taking a 2-1 lead into the fourth set.
It was in the fourth set that Altmaier changed his tactics. The World No.56 deployed the legal but rarely used tactic of underarm serve twice. Tsitsipas couldn’t keep up with Altmaier intensity on the court, which led the German star to win the set 6-3. In the fifth set, both players went all out for the win, but Altmaier was more aggressive.
He served and volleyed 14 times in the set, and that helped him beat the Greek star 7-6 (5), 1-6, 4-6, 6-3, 7-5 in four hours and twenty-six minutes, sending Altmaier to the third round. When they approached the net, Tsitsipas made sure to let Altmaier know that he didn’t like his tactics as they shook hands.
During the tense scenes, a mic caught Tsitsipas saying to the German that he deliberately targeted his body and felt disrespected by his behavior. He then pointed out that he might do the same when they meet again:
Next time, don’t wonder why I hit you, OK? No, I’m just saying if you serve underarm…if you serve underarm.
Stefanos Tsitsipas had some words with Dan Altmaier after losing to him at U.S. Open:
— The Tennis Letter (@TheTennisLetter) August 29, 2025
He’s complaining about Dan hitting an underarm serve during the 4th set.
Frosty. 🥶
pic.twitter.com/eEaPIpuApL
Altmaier withdrew from Tsitsipas, refusing to react to the former World No.3 before going on to wave to the crowd after the victory. Meanwhile, Tsitsipas left the court frustrated as he failed to reach the third round of a Grand Slam tournament this season.
The Greek star also won just two major matches this season and that came at the French Open and the US Open, while at the Australian Open and Wimbledon, he crashed out in the opening round.
Daniel Altmaier says Stefanos Tsitsipas will regret his reaction in the second round of the US Open
Stefanos Tsitsipas’ coaching team was warned for coaching him during the match, after his father, Apostolos Tsitsipas, was seen shouting instructions to him during the tense encounter against Daniel Altmaier at the US Open. Tsitsipas will end the season not playing the third round of a Grand Slam tournament for the first time since 2017.

Altmaier was asked about Tsitsipas’ reaction about his underarm serve tactics during their match. The World No.56 revealed during his interview with Sky Sports via Yahoo Sports that Tsitsipas will regret his actions in the future and that he wouldn’t have engaged in a verbal exchange if he had lost:
I know that in the heat of the moment, things can be said that wouldn’t normally be said, and then you regret them. I think that’s what online discussions are based on. I’m not a fan of them, to be honest. Even if I had lost, I wouldn’t have engaged in a verbal exchange because you need to cool down after the match. We’ll see if Tsitsipas reconsiders or maintains his opinion. For me, everything is fine. I know what I did is part of the game.
Tsitsipas has not won two consecutive matches on tour since the Barcelona Open in April. The 27-year-old has dropped outside the Top 25 of the ATP rankings following his poor run. He recently reunited with his father after parting ways with Goran Ivanisevic just weeks into their partnership.