The world number one becomes the seventh man to achieve the feat – and the third youngest behind Rod Laver and Don Budge.

Djokovic had his moments in an enthralling final but was ultimately ground down by Nadal’s intensity.

Afterwards the Serbian was typically gracious in admitting he had fallen short against a man he believes could rewrite the record books.

“He has the capabilities already to become the best player ever,” said Djokovic.

“I think he’s playing the best tennis I have ever seen him play on hard courts.

“He has improved his serve drastically. The speed, the accuracy, and of course his baseline is as good as ever.

“So he’s a very complete player.”

Having beaten Roger Federer – a winner of 16 grand slam events and widely regarded as the benchmark when discussing the greatest of all time – in the semi-finals and then faced Nadal in the title showdown, Djokovic is well-placed to compare the two.

He added: “At this point there is five, six years’ difference between them, and basically Federer has had more years on the tour, he has had more success; he has more trophies.

“He’s definitely somebody who made history in this sport. And he’s still playing as one of the best players in the world.

“On the other hand, you have Nadal who is just proving each day, each year that he’s getting better.

“That’s what’s so frustrating. He’s getting better each time you play him.

“He’s so mentally strong and dedicated to this sport. He has all the capabilities, everything he needs, in order to be the biggest ever, in my opinion.

“He has lots to come if he physically holds in the next five, six, seven years.”

Nadal was delighted to have finally triumphed in New York and was particularly satisfied to have delivered when it really mattered.

He said: “I think for the first time in my career I played a very, very good match in this tournament.

“I played my best match in the US Open at the most important moment, so I am very, very happy for that.”

The Majorca-born star was as pleased to have won in the Big Apple as he was to have claimed all four majors.

“For me it’s a dream to have the career Grand Slam but it’s even more of a dream to have won the US Open,” he said.

“It’s an unbelievable feeling because I have worked hard all my life in some difficult periods to be here but I never imagined having all four grand slams.”

On the inevitable comparisons with Federer he insisted he still had some way to go before being regarded as better than the Swiss ace, adding: “I think talk about if I am better or worse than Roger is stupid, because the titles say he’s much better than me.

“I think that will be true all my life.

“For me Roger was always an example, especially because he has improved his tennis throughout his career, and that’s a good thing that you can copy.

“So I try to do this. I know Roger and me are different, much different styles.

“And I don’t think it’s right to talk about me being better because I don’t think that.”