Novak Djokovic and Rafa Nadal will meet in the US Open final for the second year in a row after winning their semi-finals on a day of unrelenting drama and precision tennis at Flushing Meadows on Saturday.

Djokovic showed why he is the hottest player in the game right now when he saved two match points to roar back from the brink of defeat and beat Roger Federer in a five-set thriller that whipped the Arthur Ashe Stadium crowd into a frenzy of excitement.

Then Nadal, his form and confidence soaring with each match he plays, powered past Britain's Andy Murray 6-4, 6-2, 3-6, 6-2 and set up a mouthwatering rematch between the top two players in the world.

Nadal beat Djokovic 12 months ago to complete his collection of grand slam titles but the Serbian has had his measure this year.

"I've lost my last five matches against him, five finals," Nadal said. "He's obviously the favourite for the final, and I know I have to do something better than those other matches to try and change the situation."

For Djokovic, who has already won two grand slam titles this year, at the Australian Open and Wimbledon, there was just relief that he made the final after he survived a pulsating contest with Federer that could have gone either way.

Federer won the first two sets then regained his composure to lead 5-3 in the fifth.

The Swiss maestro, a five-time champion at Flushing Meadows served for the match and had two match points, but Djokovic saved them both and won the last four games to complete an incredible comeback.

"It's a sport where one wins, one loses," Djokovic said. "We have a saying, 'what doesn't kill you makes you stronger."

For Federer, it was a heart-breaking loss. He may have won more grand slam titles than any other man that has played the game but his last was at the 2010 Australian Open. Now on the wrong side of 30, he doesn't move as fast as he once could and hit a string of ugly shanks.

"Sure, it's disappointing, but I have only myself to blame," said Federer. "I set it all up perfect, but I couldn't finish it."

"It hurts, but it's fine. It could be worse. It could be a final."

Murray, 24, never really threatened Nadal although he had the consolation of taking a set off him, a feat that none of his other opponents have managed at the US Open this year.

He played aggressively, cracking 44 winners, 13 more than Nadal, but his 55 unforced errors was more than twice his opponent's total.

The Scotsman still has time on his side but he carries the added burden of 75 years of British frustration.

The World No. 4 made the semi-finals of all four grand slams this year but is still searching for his first major win.

"It's something I want to try and achieve, but if you want to judge someone's whole career based purely on slams, I would have had a terrible career," he said.

"I've still got hopefully three or four more years where I'm playing the tennis in my peak. I need to stay healthy and improve."