WASHINGTON - Fifth seed Alexander Zverev from Germany said he was "in shock" after top seed Novak Djokovic was defaulted from the US Open on Sunday.

World number one Djokovic was stunningly disqualified after accidently hitting a line judge with a ball during his round of 16 clash with Pablo Carreno Busta of Spain.

Though it was clear that Djokovic had not intended to hit the line judge, organizers nevertheless said the Serbian was disqualified in accordance with the rules.

"I think the supervisors are just doing their job, but very unlucky for Novak," said Zverev, who reached the quarterfinals by winning on Sunday. "If it would have landed anywhere else, he would have been fine."

"I don't think I have ever gotten defaulted yet in my career or in my life. No, I haven't been in a situation like that. But as I said, it's very unlucky, very unfortunate," Zverev added.

"The decision was made I think by the supervisors, and as I said, they are just doing their job. There is nothing much I can say to that. I'm a little bit in shock right now, to be honest."

Djokovic's exit means there will be a first-time Grand Slam champion in the men's draw, with Zverev among the contenders at Flushing Meadows.

"There's going to be a new Grand Slam champion. That's all I know right now. There's no past Grand Slam champions left in the draw," Zverev said.

"It's going to be one of the young guys, I think, if you count Dominic Thiem as a young guy, as well. He obviously has a chance to win. Now I think it is the time where it gets really interesting. We'll see where we go from here."