Alexander Zverev, the No 12 seed, was serving in the fourth set of his match against Jannik Sinner when he suddenly went to chair umpire James Keothavong and pointed toward the fan in the crowd.
"He just said the most famous Hitler phrase there is in this world," Zverev told Keothavong.
"It’s not acceptable."
The umpire turned around and asked the fan to identify himself, then asked fans to be respectful to both players.
But during the changeover shortly after Zverev's serve, the culprit was identified by spectators seated near him and removed by security.
The player said after the match that he's had fans make derogatory comments before, but not involving Hitler.
"He started singing the anthem of Hitler that was back in the day," Zverev said.
"It was 'Deutschland über alles' (Germany above all) 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."
US Tennis Association spokesman Chris Widmaier said: "A disparaging remark was directed toward Alexander Zverev.
"The fan was identified and escorted from the stadium."
Zverev went on to drop that set when he began to struggle with the humid conditions.
But he recovered to win the fifth set, wrapping up the match that lasted four hours, 41 minutes - and will now play defending US Open champion Carlos Alcaraz in the quarter-finals.
Zverev added it wasn't hard to move past the fan's remark.
"It’s his loss, to be honest, to not witness the final two sets of that match."
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