Novak Djokovic broke down in tears after suffering a stunning US Open first-round defeat to Argentina’s Mariano Navone, raising fresh questions about whether age is finally catching up with the 39-year-old tennis great.

The 24-time Grand Slam champion struggled physically throughout the dramatic encounter in humid New York conditions, at one point vomiting into a towel bin before eventually losing 7-6 (7-5), 5-7, 4-6, 6-2, 6-1.

Despite his physical struggles, Djokovic displayed the fighting spirit that has defined his extraordinary career, battling through the opening sets before Navone seized control and completed one of the biggest victories of his career.

The defeat marked Djokovic’s first-ever loss in the opening round at the US Open and his first first-round exit at a Grand Slam since 2006.

“I think it was obvious that it was an awful feeling on the court for me,” Djokovic said after the match. “I don’t want to take too much out of Mariano’s win. Congrats to him, he’s a nice guy and a fighter – but I didn’t enjoy myself.”

Djokovic showed his trademark class by congratulating the 25-year-old Navone, but struggled to contain his emotions afterwards. He appeared close to tears as he made his way back towards the locker room.

The defeat also ended Djokovic’s latest pursuit of a record 25th Grand Slam singles title, which would have moved him clear of Australian legend Margaret Court.

Is age finally catching up with Novak Djokovic after his heartbreaking US Open exit?