Novak Djokovic was fuming at Arthur Ashe Stadium.

The No. 2 seed at the U.S. Open was incensed when a fan yelled “Out!” during a live volley with American Taylor Fritz, causing him to lose focus and the point.

Djokovic appeared to shout at someone in his own box as the outburst caused him to cede the breakpoint and eventually the game.

The Serbian star held on to defeat the No. 9 seed 6-1, 6-4, 6-4.

It’s not the first case of fans getting unruly during the tournament.

During the Monday night session, a fan was kicked out of Ashe for reportedly yelling a Hitler phrase at German-born Alexander Zverev.

“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,” Zverev said.

“I think he was getting involved in the match for a long time, though. 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 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.”

Djokovic will next face either Np. 10 seed Frances Tiafoe or Ben Shelton in the semifinal.