Djokovic says Alcaraz pushes him to the limit

But the man likely to be standing in his way is Alcaraz, the defending champion who beat Djokovic in the Wimbledon final last month.

Djokovic got a measure of revenge when he outlasted the 20-year-old Spaniard in a near four-hour final in Cincinnati a week ago.

The duo may be at the opposite end of their careers but they have already built a rivalry which looks set to endure for as long as Djokovic, 36, continues to pick up a racket.

"He's always pushing me to the limit," said the Serbian. "I think I do to him pretty much the same thing. That's why we produced a memorable final.

"It was one of the best, most exciting, and most difficult finals I was ever part of in best-of-three, no doubt, throughout my career.

"That's why I fell on the ground after I won the match because it felt like winning a grand slam, to be honest. The amount of exchanges and rallies. It was physically so demanding and gruelling that I felt very exhausted for the next few days.

"Those are kind of the moments in matches that I still push myself on a daily basis, day in and day out, practice, sacrifice, commitment. At 36, I still have the drive."

If Djokovic wins his first-round match, against Frenchman Alexandre Muller, he will overtake Alcaraz to become world No.1 again.

Alcaraz, the top seed, starts his campaign on Tuesday against Dominik Koepfer of Germany.

Iga Swiatek opens proceedings on Monday against Rebecca Peterson of Sweden as she bids to defend the title she won last year.

"On one hand you always want to kind of take experience from last year, find all these positive things that happened, take strength from that," said the world No.1 from Poland.

"On the other hand you have to remember that it's a totally different story. A lot can happen during like these 12 months.

"So I try to take everything step by step, not really go forward with my thoughts, think that I need to do something more because last year I won."