Djokovic, 38, beat Tien, 6-1, 7-6, 6-2 to improve to 19-0 in US Open first-round matches, tying Roger Federer for first all-time. But he labored with low energy, a nasty blister on his right big toe and Tien’s level, especially in the second set.

It seems the Serbian star is starting to feel the weight of age, but he's still clinging to his talent and whatever energy he has left.

Former World No.1 Novak Djokovic has ascended to the mountaintop in the tennis community, having etched his name in history as one of the best players of all time.