Novak Djokovic considers his mental state just as important as his physical condition when it comes to being prepared to play his best at age 36.

“Mentally there is probably a lot more that I’m dealing with in my private life than was the case 10 years ago. But that’s the beauty of life. Things are evolving, moving on,” said Djokovic, who will try to take another step toward what would be a 24th Grand Slam title when he faces Ben Shelton in the US Open semi-finals on Friday.