Alexander Zverev's late-night US Open round of 16 match against Jannik Sinner was marred by a racial slur made against the German No 12 seed.<br /><br />Zverev and Sinner were embroiled in an enthralling fourth-round tie in the early hours of the morning in New York when the former made a complaint to the umpire about a comment he heard in the seconds before a point.<br /><br />'He just said the most famous Hitler phrase there is. It is unacceptable,' Hamburg-born Zverev told British umpire James Keothavong after hearing a slur from the crowd.<br /><br />Following the game, Zverev told a reporter what the supposed fan had said.<br /><br />'He started singing the anthem of Hitler that was back in the day. It was `Deutschland über alles' and it was a bit too much,' the Hamburg native said. <br /><br />'I love it when fans are emotional. But I think me being German and not proud of that history, it's not 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,' he added. <br /><br />In response, the umpire turned around in his chair to directly address the most expensive courtside seats, asking the culprit to identify himself.<br /><br />When nobody owned up, Keothavong announced to the whole crowd to respect the players, while security was dispatched into the area to try and remedy the unsavory situation.<br /><br />Play continued, before cameras then cut back to the stands a few minutes later to show a middle-aged male being spoken to by security and then led out of the arena - much to the delight of the fans around him.<br /><br />It is unclear exactly what was allegedly said by the man, or if the man pictured by ESPN cameras was the fan alleged to have made the slur.<br /><br />It is not the first crowd incident at this year's US Open, with Daniil Medvedev openly criticizing the supporters' noise after one of his matches.<br /><br />'Thanks to all those who didn't yell between my first and second serve,' he said to the crowd after beating Sebastian Baez.<br /><br />'However, there was a spectator, maybe he has a girlfriend or a wife who I don't know how she will sleep… He was particularly excited and would spend the night saying Vamos, vamos, vamos, without ever stopping. I'm sorry for him.'<br /><br />Elsewhere, other fans have commented on the 'feral' atmosphere being offered up - especially on the Labor Day weekend in the Big Apple.<br /><br />In the match itself on Monday night, Zverev won the first set against his Italian opponent Sinner, who is ranked sixth and headed into the fourth round match as the favorite.<br /><br />Sinner fought back to level at one-set-all before Zverev made the most of his opponent's injury struggles to take the third set.<br /><br />When all looked lost for Sinner with 1 a.m. approaching in the Big Apple, though, he won the fourth set to force a decider.
