Frances Tiafoe and Taylor Fritz set up an all-American semifinal at the U.S. Open with victories Tuesday, guaranteeing the United States a man in the title match at the country’s Grand Slam tournament for the first time in 18 years.

The 20th-seeded Tiafoe made it to the final four at Flushing Meadows for the second time in three years when his quarterfinal opponent, Grigor Dimitrov, stopped playing because of an injury in the fourth set. Tiafoe was leading 6-3, 6-7 (5), 6-3, 4-1 with midnight approaching when Dimitrov retired from the match, providing an anticlimactic ending to a contest that was not necessarily of the highest quality.

“It’s not the way I want to get through,” Tiafoe said, “but obviously happy to get through. Another semifinal here. Incredible.”

Just one glimpse of the sort of uneven play from both: Dimitrov held three set points in the tiebreaker at 6-3. On the first, he double-faulted. On the second, he double-faulted again. On the third, Tiafoe double-faulted, handing over that set.

Hours earlier, Fritz advanced in a far more satisfying way, watching one last errant forehand from his higher-ranked, more-accomplished opponent land wide. Fritz dropped his neon-colored racket, clenched both fists and screamed, “Come on!”

He gathered himself and his equipment, walked to the net for a hug with No. 4 Alexander Zverev, who twice was a Grand Slam runner-up, then stepped to the center of Arthur Ashe Stadium, spread his arms wide and yelled again, “Come on!”

After years of climbing the rankings, of becoming the top American man in tennis, of coming close to making a breakthrough at one of his sport’s four most important events, Fritz finally came through at home, beating Zverev 7-6 (2), 3-6, 6-4, 7-6 (3) to reach a major semifinal for the first time.

The 12th-seeded Fritz, a 26-year-old from California, entered the day with an 0-4 record in Slam quarterfinals.

Now on Friday, he will take on longtime friend Tiafoe, a 26-year-old from Maryland who lost to eventual champion Carlos Alcaraz in the 2022 U.S. Open semifinals.

Fritz holds a 6-1 head-to-head edge over Tiafoe as pros.

“It’s the biggest match of me and Taylor’s life. We’ve known each other for so long. I’ve been playing against him since (14-and-under tournaments),” Tiafoe said during an on-court interview. “So to be able to play him here … is going to be awesome. I know we’re two Americans, but I hope you’re all with me come Friday.”

The Fritz-Tiafoe showdown — “That could be crazy,” Fritz said, before he knew whom he’d face next — is the first semifinal between a pair of American men at any major since 2005, when Andre Agassi defeated Robby Ginepri in New York.

No American man has won a Grand Slam singles trophy since Andy Roddick triumphed at the U.S. Open in 2003; Roddick was the last man from the United States in the U.S. Open final, losing to Roger Federer in 2006.

Dimitrov, who was seeded No. 9, had played a five-setter in the fourth round and appeared to be fading late in the third set against Tiafoe, grabbing at his left hamstring, walking gingerly between points and hitting serves much slower than earlier in the evening. After that set, Dimitrov was visited by a trainer and then headed to the locker room for treatment.

He returned to the court for the start of the fourth set but wasn’t able to move properly and eventually quit. Dimitrov, a 33-year-old from Bulgaria who has appeared in three major semifinals, wouldn’t say afterward exactly what was wrong, only that it was an accumulation of things.

“Just a disappointing moment for me,” Dimitrov said. “I need to reassess a couple of things.”

The other men’s quarterfinals will be played Wednesday: No. 1 Jannik Sinner vs. No. 5 Daniil Medvedev, and No. 10 Alex de Minaur vs. No. 25 Jack Draper.

In the women’s bracket, No. 13 Emma Navarro of the U.S. reached her first Grand Slam semifinal by taking the last six games in a 6-2, 7-5 victory over No. 26 Paula Badosa and next faces No. 2 Aryna Sabalenka.

Fritz used his usual blend of big serving, winning 20 of 21 points when his first serves landed in during the fourth set, and big forehands, but he also was effective at the net — winning 16 of 24 points when he pushed forward — and returned well enough to accumulate 10 break points.

Even though Fritz only converted two of those break chances, it meant he constantly put pressure on Zverev, a German who made it to the finals of the U.S. Open in 2020 and the French Open this year.

Fritz’s latest quarterfinal loss came in July at Wimbledon against Lorenzo Musetti. The other three? Two came against 24-time Slam champion Novak Djokovic; the other against 22-time Slam champion Rafael Nadal.

One was at last year’s U.S. Open against Djokovic, who went on to win the title. Djokovic was eliminated this time in the third round last week; Nadal sat out the tournament.

Fritz’s coach, Michael Russell, said those past stumbles were not a topic of conversation before this quarterfinal.

“It’s cool I’m in the semis. But I very much have the mindset of ‘the job’s not done,’” Fritz said. “A question I got asked pretty much every time I lost in my quarterfinals was, ‘What’s it going to take to go further?’ And the answer I gave was always: Just keep putting myself in these situations, and I’ll become more comfortable in these situations and get better. That’s definitely what happened now. The quarterfinals didn’t feel like, I don’t know, this big thing to me like it has been, I guess, in the past.”