NEW YORK -- Frances Tiafoe and Taylor Fritz set up an all-American semifinal at the US Open with victories Tuesday, guaranteeing the host country a men's finalist in its Grand Slam tournament for the first time since 2006.

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, 7-6 (5), 6-3, 4-1 when Dimitrov retired from the match.

Hours earlier, Fritz watched one last errant forehand from No. 4 Alexander Zverev land wide, dropped his neon-colored racket, clenched both fists and screamed, "Come on!"

Fritz gathered himself and his equipment, walked to the net for a hug with his higher-ranked, more-accomplished opponent, 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.

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 and walking gingerly between points. 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.

The Fritz-Tiafoe semifinal -- "That could be crazy," Fritz said -- is the first 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 US Open in 2003; Roddick was the last man from the United States in the US Open final, losing to Roger Federer in 2006.

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

The Associated Press contributed to this report.