As Stefanos Tsitsipas missed the final return, the ball sailed past the baseline, and the crowd erupted. Daniel Altmaier had done it. The German lay flat on the court, taking in the moment as the commentator confirmed the final score in that grueling five-set battle: 7-6(7-5), 1-6, 4-6, 6-3, 7-5. When Altmaier finally rose and walked toward the net for what should have been a routine, sportsmanlike handshake, the atmosphere shifted. Given the drama of the US Open, it would’ve been surprising if a few words exchanged there came without their own tension anyway.

Displeased with the German’s underarm serve in the fourth set, the Greek star was caught warning his opponent at the net: “Next time, don’t wonder why I hit you, ok?” He was referring to an earlier incident during the match when he had fired a forehand toward Altmaier’s body, a shot he later apologized for on court. As the conversation continued, Tsitsipas explained, “No, I’m just saying if you serve underarm… if you serve underarm,” after noticing Altmaier’s apparent surprise.

The reason behind Tsitsipas’s frustration lay in Altmaier’s strategy. Aware of the Greek’s emotional volatility, the German mixed up the rhythm with constant changes of pace and precise shot-making. In the fourth set, he even threw in multiple underarm serves; a tactic now considered legal and increasingly common on tour, but still perceived by some as cheeky or disrespectful. While underarm serving demands immense skill and risk, Tsitsipas clearly saw it as an insult. He kept his cool during play, apart from that one forehand aimed at Altmaier. The latter, however, wasn’t interested in prolonging the spat.

He dismissed Tsitsipas’s words, walked over to shake hands with the chair umpire, and then turned to the crowd with both arms raised, celebrating his hard-earned progression to the next stage. For the 26-year-old German, this was a career milestone. It was his first time reaching the third round at the US Open after coming through another marathon against Serbia’s Hamad Medjedovic in the opening round (7-5, 6-7(3), 7-6(7), 6-7(5), 6-4) in a match lasting 4 hours and 46 minutes.

Next up, Altmaier will face Australia’s Alex de Minaur on Friday. As for Tsitsipas, he certainly had a bad day in the office, and the reason is more than just this defeat.

It just wasn’t Stefanos Tsitsipas’ day!

Stefanos Tsitsipas, who has spent most of his career under the guidance of his father Apostolos, briefly turned to Goran Ivanisevic earlier this season before reuniting with his dad in July. But during Tsitsipas’ second-round battle with Daniel Altmaier, father Apostolos himself made headlines by picking up what may be the first coaching warning since the rule was largely relaxed.

His offense? Shouting instructions while Stefanos was on the far end of the court — something that, despite broader coaching allowances, remains against the guidelines. The warning ultimately had no bearing on the outcome, serving only as a minor footnote on a challenging day for the two-time Grand Slam finalist, who had already put in a hard shift in his US Open opener, battling past France’s Alexandre Muller 4-6, 6-0, 6-1, 7-6 (5) on Court 7.

Perhaps a difficult conversation is on the cards for the Tsitsipas family as this wasn’t the first time the elder Tsitsipas was called out for shouting coaching instructions. It happened three years ago as well, when the rules still hadn’t been relaxed. What are your thoughts on the incident? Let us know in the comments. For minute-by-minute updates from the US Open, head to our EssentiallySports’ Live Blog