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Both men were looking to take a huge step towards ending the United States' 21-year wait for a male champion at Flushing Meadows, and it was Tiafoe who took the opener despite giving up an early break, hitting back with two of his own in the fifth and seventh games.

Fritz rallied to take the second set, but Tiafoe came on strong again in the third, harnessing the support of the crowd and using his power to dominate rallies.

An early break proved enough for Tiafoe to go 2-1 up, and he found himself two games from victory at 4-4 in the fourth set.

However, a missed forehand at deuce gave Fritz set point, and Tiafoe then failed with an attempted drop shot to let his opponent force a decider.

The momentum switched from then on, with Fritz never looking back. He hit a massive backhand winner in his first return game of the decider to break, and though he later let a double-break advantage slip with a double fault, that was a momentary blip as he ran away with the fifth set.

After the win, Fritz hailed his coach Michael Russell for the calming effect he was able to exert after a tough start to the encounter.

"I felt I wasn't doing anything wrong, I was just getting overwhelmed," Fritz said. "I was freaking out a little bit and he told me to keep doing what I was doing, accept it was OK and keep making him do it. That helped to calm me down and let me know I was doing the right thing."

Among male players representing the United States, Fritz, at the age of 26 years and 313 days, is the second-oldest in the Open Era to reach a maiden grand slam final, after MaliVai Washington (27 years, 15 days) at Wimbledon in 1996.

It took Fritz 33 main-draw campaigns to reach his first Major final, with only David Ferrer (42), Stanislas Wawrinka (36) and Kevin Anderson (34) requiring more in the Open Era.

He could become the first home winner of the US Open since Andy Roddick in 2003 when he faces Sinner in the showpiece match.