Novak Djokovic provided irrefutable proof that he is the world's best player right now and perhaps on his way to becoming one of the greatest ever with a 6-2 6-4 6-7 6-1 victory over Rafa Nadal in the U.S. Open final Monday.

In claiming his third grand slam title of an amazing season, Djokovic produced an incredible display of shotmaking and courage when his body started to wilt during a classic slugfest at Flushing Meadows that lasted four hours and 10 minutes.

The Serbian's lower back and his ribs were aching and his legs were starting to cramp up, but he ignored the pain and focused all his energy on the muscular Nadal, who was threatening to mount a comeback.

The Spaniard won the third set in a tiebreaker to keep the match alive and the raucous crowd at the Arthur Ashe Stadium were screaming their lungs out in the hope that it might go to five sets.

Both players appeared on the brink of total exhaustion but Djokovic remained calm and composed.

In the big events and matches, the winner is decided by small margins, a couple of points, he explained after claiming his first U.S. Open title and fourth major overall.

I guess the winner is the one that believes in victory more than the other.

The victories have been flowing thick and fast for Djokovic this year. He has won 10 titles this season, including the Australian Open, Wimbledon and the U.S. Open, and no-one seems to know how to beat him, least of all Nadal.

Twelve months ago, the Spaniard was on top of the world after defeating Djokovic in New York to complete his own collection of grand slam titles, but now he can only look on as his rival has replaced him as the top dog in men's tennis.

Djokovic has usurped Nadal as the world number one and beaten him in six finals this year, including at Wimbledon and the U.S. Open.

Six straight loses, for sure that's painful but I'm going to work every day until that changes, Nadal said.

So I have a goal. It's going to be tough to change the situation, but the goal is easy to see.

The pair produced a final of the highest quality, with some incredible rallies and shotmaking that whipped the center court crowd into a frenzy. Nadal had his chances but it was Djokovic who won the key moments.

EPIC GAME

No matter how hard he tried, Nadal could not find a way to get on top of the Serbian, who had saved two match points in his epic semi-final win over Roger Federer to show that he has all the instincts of a prize fighter to go with his sublime skill.

In the opening set, the defending champion jumped out to a 2-0 lead, only to be reined in by Djokovic, who kept the Spanish left-hander under constant pressure with some monster returns that landed right at his feet.

It was a tough match, physically, mentally, everything, Nadal said.

I fought until the last point. I tried my best at every moment. I am happy with a lot of things, much happier than the previous matches against him.

Djokovic, mixing power with some delicate chip shots that often left Nadal in two minds, reeled off six straight games to take the opening set after 53 minutes but suddenly found himself down 2-0 again at the start of the second.

He broke back after a titanic third game that lasted more than 17 minutes and included eight deuces to lead 4-2. Nadal got back to 4-4 but another sloppy service game cost him the set.

The third set was the longest, lasting 84 minutes. Both players were broken three times but Djokovic led 6-5 and had the chance to serve out the match.

To his credit, Nadal fought back and forced the match into a fourth set but he was drained by the effort.

Djokovic was tired as well and called for a medical timeout at the start of the fourth set but he recovered quickly and ran away with the set to seal his first U.S. Open title and the fourth of his career.

Only the French Open remains missing from his trophy cabinet.

I still want to win many more events, many more major events, Djokovic said.

It would be unbelievable to be able to complete the grand slam, to win the French Open. It's something that is definitely an ambition, but it's going to take time.