Rafael Nadal cruised into the US Open final with a 21-match hardcourt unbeaten streak while world number one Novak Djokovic had to withstand a five-set, limit-testing struggle to join him.

Second-ranked Spaniard Nadal, whose 12 Grand Slam titles include the 2010 US Open, routed French eighth seed Richard Gasquet 6-4, 7-6 (7/1), 6-2, to reach his third final in four years. Nadal missed the 2012 event with knee injuries.

"Just amazing," Nadal said. "After what happened last year, to have the chance to play in the final on Monday is a dream for me. It has been two amazing weeks for me."

Serbian six-time major winner Djokovic outlasted Swiss ninth seed Stanislas Wawrinka 2-6, 7-6 (7/4), 3-6, 6-3, 6-4 after four hours and nine minutes to reach his fourth US Open final in a row, fifth overall, and 12th Slam final.

Nadal leads Djokovic 21-15 in their personal rivalry, which will move past John McEnroe and Ivan Lendl as the most-played matchup in the Open era.

Nadal won their most recent meetings in a five-set French Open semi-final and last month's Montreal semi-finals and has split two US Open finals with him, winning in 2010 to complete a career Grand Slam but losing a year later to give Djokovic his first trophy on the Flushing Meadows hardcourts.

"Novak is an amazing competitor," Nadal said. "His results say it. He's one of the best players I've ever seen.

"He's a great champion. It will be a tough final for me but I hope to be ready for that."

Nadal dropped serve for the first time in the fourth game of the second set of his semi-final, ending his streak of 73 held service games at the US Open and a run of 88 in total stretching to the ATP Cincinnati Masters semi-finals.

But it was the only break Nadal surrendered, and when he overwhelmed the Frenchman in the tie-breaker, it was clear he was in total command. He finished after two hours and 21 minutes.

Nadal, who has won nine titles since ending a seven-month layoff to rest his knees, denied Gasquet's bid to become the first Frenchman in a US Open final since Cedric Pioline in 1993. It was his first Slam last-four since Wimbledon in 2007.

For his part, Djokovic admitted that he was not even the best player on the court for much of his match, but said he was able to raise his game when it mattered most to subdue stubborn Wawrinka, in his first Grand Slam semi-final.

"It was obvious Stan played more aggressive. He played better tennis," said Djokovic. "I was trying to hang in there, to adjust. It was tough on both of us. I had to run a lot. I had to find my rhythm.

"I was just so fortunate to play my best tennis when I needed to."

An epic third game of the fifth set lasted 21 minutes, Wawrinka fighting off five break points to hold for a 2-1 lead after 30 points, reaching deuce 12 times.

The Swiss denied Djokovic break points with forehand, backhand and service winners as well as two netted backhands by the Serb before closing out the game on a service winner.

"I was thinking, 'Whoever wins this game is going to win this match,'" said Djokovic. "After he won that game I was thinking, 'I have to fight against those odds.'"

But Djokovic finally capitalized on his eighth break point of the last set when Wawrinka swatted a backhand beyond the baseline to give him a 3-2 lead.

The reigning Australian Open champion had converted only 3-of-18 break points up to that moment, but took the critical break and held the rest of the way to advance, dropping Wawrinka to 0-13 against world number ones.

"It was a great tournament for me," Wawrinka said after his first Grand Slam semi-final, a run that included his quarter-final ouster of defending champion Andy Murray.

"Tough match to have lost. I gave everything."

The victory ensured Djokovic will stay atop the rankings after the US Open no matter how he fares in the final.

Djokovic improved to 13-2 with his 11th victory in a row over Wawrinka, who also pushed him to 12-10 in the fifth set in a fourth-round matchup at the Australian Open.