Frances Tiafoe came from two sets and a break down to beat fellow American Alex Michelsen in a thrilling comeback to reach the US Open semi-finals.

Eleventh seed Tiafoe was outplayed by world number 46 Michelsen for the first half of the match, but battled back from 5-3 down in the third set - with his opponent serving for the match - to ignite a remarkable turnaround.

In a final set of multiple breaks and swings of momentum, Tiafoe triumphed in the 10-point tie-break to win 5-7 3-6 7-5 6-3 7-6 (10-6).

Victory means 28-year-old Tiafoe reaches his third US Open semi-final in five years, where he will play defending champion Carlos Alcaraz or American eighth seed Ben Shelton.

Michelsen, 22, who was competing in his first Grand Slam quarter-final, was in tears as the pair embraced after a match which lasted four hours and 38 minutes.

"He's a hell of a player and he easily could have won today. Shout out to Alex Michelsen," said Tiafoe.

"Everyone was asleep in the first couple of hours, I was too. As it went along the energy was incredible as it is always. You guys are rooting for me and I appreciate that."

'I'm a different person' - Tiafoe's transformational year

Tiafoe is hoping to reach the final at Flushing Meadows for the first time, following semi-final defeats by Alcaraz in 2022 and Taylor Fritz in 2024.

But it was a straight-set third-round loss to Jan-Lennard Struff in last year's tournament which brought about a change in coach - and mentality.

"This time last year he was losing matches because of his fitness, now here we are four hours and 40 minutes into a match and he's raining down the fastest serve of the match," former Grand Slam doubles champion Ryan Harrison told Sky Sports.

"This is why he put the hard work in at the gym when nobody's watching. At the end of last year when he was having to hear all the chatter about his commitment, things he wasn't doing well - at 28 years old it's so hard to make a change like that, and his willingness to go through the process.

"For him to go through all that work, to fight to put himself in this position its great to see."

While it has taken until now for Tiafoe's renewed work-ethic to bear fruit in a major, he is unequivocal when asked how he compares to the player that reached the last four previously in New York.

"I'm just a different person in general," he said.

"Those two runs were great, something I will cherish forever, but I'm not that person who I was when I made one in 2022 and when I made one in 2024. I'm not that person.

"I think I've been so routine-oriented all year, just continuously on a routine. Ideally you want to make every day feel the same."

Unseeded Michelsen came into the match in fine form, having not dropped a set at the tournament prior to facing Tiafoe, and grasped the momentum in the first set.

After the pair traded breaks of serve early in the match, Michelsen got the deciding break at 6-5 in a set where he fired 15 winners to Tiafoe's four.

Michelsen continued to have the upper hand, with his backhand proving decisive on key points and, after taking the second set, he went up a break early in the third.

It was not until Michelsen was serving for the match at 5-4 that nerves began to hit. He served two double faults and Tiafoe broke to level, won the set and took the opening three games of the fourth set.

After holding Michelsen off, Tiafoe took the match to a deciding set where the pair traded multiple breaks of serve - invigorating the spectators on Arthur Ashe Stadium.

A fan favourite, Tiafoe thrived off the energy of the New York crowd as he then got the better of the tie-break to seal his fourth five-set victory at a major in 2026.

"He's a great guy for consoling me in that moment," said Michelsen of their post-match embrace.

"I was trying to keep it together, and I didn't do a good job of that. He was saying a lot of nice personal things.

"I've got a lot of time to grow physically and mentally. I'm going to be here again. I know it."