‘He just said the most famous Hitler phrase there is. It is unacceptable,’ Zverev told British umpire James Keothavong after hearing the slur from the crowd.
Keothavong turned around and urged fans inside Arthur Ashe Stadium to be respectful to the players as security were seen kicking out a middle-aged man.
It is unclear exactly what the spectator said, but Zverev claimed after the match that the person was singing a song associated with the former Nazi Party leader.
‘He started singing the anthem of Hitler that was back in the day,’ Zverev said. ‘It was ‘Deutschland über alles’ and it was a bit too much.
‘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.’
A spokesperson from the US Tennis Association said: ‘A disparaging remark was directed towards Zverev. The fan was identified and escorted from the stadium.’
Zverev ended up beating Sinner in a match which lasted almost five hours and he will next face world No.1 and title holder Carlos Alcaraz in the quarter-finals.
The 26-year-old is looking to lift his maiden Grand Slam title and was a finalist at Flushing Meadows three years ago.
In the other quarter-finals, American home favourite Taylor Fritz takes on 23-time major champion Novak Djokovic while there is an all-Russian battle between Daniil Medvedev and Andrey Rublev after the latter beat Britain’s Jack Draper.
Meanwhile, 10th-seed Frances Tiafoe faces fellow American Ben Shelton for a spot in the last four.