Djokovic is bidding to become the first man since Rod Laver in 1969 to win the calendar grand slam but said he thought he heard booing from the crowd as he survived a scare to win 6-1 6-7 6-2 6-1.
“I didn’t know what they were chanting honestly. I thought they were booing,” he told reporters after the match.
“I don’t know, it was not ideal atmosphere for me to tell you that. But I’ve been in these particular atmospheres before, so I knew how to handle it.
“I mean, obviously you always wish to have crowd behind you, but it’s not always possible.
“That’s all I can say. I mean, I don’t know. I’ve been focusing on myself and what I need to do. I guess I have to just see how it feels on the court and try to keep it together. That’s all I can do.”
It’s unclear whether fans were booing the Serbian or whether they were chanting “Rune” in support of his Danish opponent.
Rune himself was confused by what he initially thought was booing but said he was happy when he realized many were just cheering on the underdog.
“Actually, at one point, they were cheering for me; another point, they were booing. I was like, ‘What is going on?'” he told reporters.
“All of a sudden, after the match I heard they said ‘Rune.’ When I heard that, I was happy because I didn’t understand it in the match. As I said, it was a crazy crowd, the best I’ve ever felt in my life.”
‘I am very excited’
Djokovic has already won the Australian Open, French Open, and Wimbledon this year and needs just one more victory at the last slam of the year to complete the epic feat.
Triumph at the US Open would also take the 34-year-old to 21 major titles, surpassing Roger Federer and Rafael Nadal who each have 20 majors to their name.
“Making history in this sport is of the greatest importance to me, particularly at this stage of my career. And playing and trying to win as many grand slams is the highest priority in my tennis season.”
He said he had “ran out of gas” at the Summer Olympics but is raring to go again after a break.
“Pressure is a privilege. I have grown and kind of developed throughout my career to really handle pressure in the right way,” he added. “But nothing is guaranteed.
“I like to have adversity. I like to have expectations and pressure and, you know, in a way it draws the best out of me. So, yeah, hopefully, I can have a fantastic couple of weeks.”