A bit of off-court drama mixed itself into the US Open Round of 16 matchup between Alexander Zverev and Jannik Sinner on Monday night.

Zverev, the top-ranked German player in the world, approached the chair umpire during the fourth set of the match and claimed a fan was uttering a Nazi phrase between points. The fan was soon identified and removed from the stadium.

“He started singing the anthem of Hitler that was back in the day,” Zverev said, via the Associated Press. “It was ‘Deutschland über alles' and it was a bit too much.”

“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 I think him sitting in one of the front rows, I think a lot of people heard it. So if I just don't react, I think it's bad from my side.”

Zverev was able to shake off the distraction for a thrilling five-set US Open win over Sinner, though he did drop the fourth set after making the chair umpire aware of the situation. He said that fans have used demeaning language toward him before but never anything involving Hitler.

It's unfortunate that this match was slightly overshadowed by the incident, given the quality that both players showed. With the win, Alexander Zverev advanced to the third US Open quarterfinal of his career. He'll play top-seeded Carlos Alcaraz on Wednesday for a spot in the US Open semifinals.