Daniil Medvedev upset defending champion Carlos Alcaraz in an enthralling semi-final duel to reach the US Open final on Friday.

Russian third seed Medvedev set up a rematch of his 2021 victory over Novak Djokovic after ousting Alcaraz 7-6 (7/3), 6-1, 3-6, 6-3 in a gripping 3hr 19min battle on the Arthur Ashe Stadium court.

Spanish star Alcaraz had been hoping to become the first man to successfully defend the US Open since Roger Federer in 2008, eyeing a blockbuster final against 23-time Grand Slam singles champion Djokovic on Sunday.

But Medvedev -- who shattered Djokovic's dream of a calendar year Grand Slam two years ago by beating the Serb in straight sets in the final in New York -- once again tore up the script.

The 27-year-old from Moscow had said before Friday's semi-final he would have to deliver an "11 out of 10" performance to beat Alcaraz, who had defeated the Russian comfortably in two previous meetings this season.

Medvedev was to prove as good as his word over the course of a high-quality duel that is surely a contender for match of the tournament.

Medvedev completed victory in the ninth game of a nail-biting fourth set, smashing a desperate return from Alcaraz to convert his fourth match point.

"Amazing, especially beating someone like Carlos," Medvedev said. "Before the match for sure I had a lot of doubts after losing easily to him twice this year.

"I said I needed to play 11 out of 10 - I played 12 out of 10, except for the third set."

Medvedev had grabbed the early initiative by taking the first set on a tie-break after neither player gave up any break point opportunities in the opening frame.

While Alcaraz looked instantly in the groove, mixing his thunderous groundstrokes with several of his signature drop shots, it was Medvedev who prevailed in the tie-break.

Buoyed by that early breakthrough, Medvedev raced away with the second set, breaking Alcaraz in the second game for a 2-0 lead and then clinching another break in the sixth game with a jaw-dropping running backhand winner down the line that fizzed past his opponent.

That left Medvedev 5-1 up and he duly served out comfortably to take a two-set lead.

Alcaraz hit back to claim the third set when Medvedev sent a return into the net, which took it into the fourth set.

The decisive break came in the sixth game, Medvedev taking a 4-2 lead with another glorious backhand return of serve that Alcaraz was unable to deal with.

Both men then held serve to leave Medvedev serving for the match at 5-3.

Alcaraz bravely saved three match points but Medvedev unleashed a corking serve on the fourth match point that the Spaniard could only manage a looping return to.

Medvedev hammered a forehand into the corner and although Alcaraz was able to get it back, Medvedev was waiting at the net to smash an unstoppable winner.