A fan was ejected from the US Open on Monday after Germany's Alexander Zverev protested about the words of a Nazi-era anthem being shouted from the stands.
Zverev was serving in the fourth set of his last 16 victory over Italy's Jannik Sinner on the Arthur Ashe Stadium when the drama unfolded.
The 12th-seeded Zverev approached chair umpire James Keothavong to complain about the alleged catcall.
"He just said the most famous Hitler phrase there is in this world," Zverev told the umpire. "This is unbelievable."
Keothavong consulted with security officials in an attempt to identify the culprit.
Eventually a man wearing a blue baseball cap was singled out and ordered to leave the arena.
Zverev later told reporters he had heard the fan singing the opening words of Germany's Nazi-era anthem -- "Deutschland Uber Alles".
"He started singing the anthem of Hitler that was back in the day – Deutschland Uber Alles – it was a bit too much," Zverev said.
"He was getting involved in the match for a long time and I don't mind it. I love when fans are loud, I love when fans are emotional but I think me being German, and not really proud of that history, it's not really a great thing to do.
"And him sitting in one of the front rows, a lot of people heard it. If I just don't react I think it's bad from my side."
Zverev however said he did not let the incident rattle him, and he duly went on to complete a memorable victory.
"Look for me it's not a very smart guy, the guy who did it," Zverev said. "At the end of the day I said what I said, the umpire said 'Okay we're going to get him out' and that's what he did.
"It's his loss because he didn't get to watch the final two sets."
The late-night US Open crowds on the 23,000-capacity Arthur Ashe Stadium are famously boisterous but have been criticised during this year's tournament.
Former Australian professional Rennae Stubbs said shortly after the Zverev incident on Monday that there were fans at night sessions that were "not good."
"I love the fans but at this point there are some bad characters," Stubbs wrote on X, the social media site formerly known as Twitter.
"I had a drink thrown on me last night by a drunk fan who was fighting with her boyfriend. Now we got someone yelling Hitler slurs! Wtf? Come on peeps."
German player Laura Siegemund also vented at the Arthur Ashe crowd after her first round defeat to Coco Gauff last week.
"They had no respect for me, no respect for the way I played, no respect for the player that I am, they had no respect for good tennis," a tearful Siegemund said.
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