NEW YORK — Frances Tiafoe and Taylor Fritz secured an all-American semifinal at the US Open with their victories on Tuesday, giving the host country the first time since 2006 that it will have a male finalist at the Grand Slam tournament.

The 20th-seeded Tiafoe reached the last four at Flushing Meadows for the second time in three years when his quarterfinal opponent, Grigor Dimitrov, retired with an injury in the fourth set. Tiafoe led 6-3, 7-6(5), 6-3, 4-1 when Dimitrov retired from the match.

Hours earlier, Fritz saw a final failed forehand from No. 4 Alexander Zverev land wide of the ball, dropped his neon-colored racket, clenched both fists and shouted, “Come on!”

Fritz gathered himself and his gear, walked to the net for an embrace with his higher-ranked, more experienced opponent, then strode to the center of Arthur Ashe Stadium, spread his arms wide and shouted again, “Come on!”

After years of climbing the rankings, becoming the top American tennis player and coming close to breaking through at one of the four major events in his sport, Fritz finally recorded a home win by 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 player from California, entered the day with an 0-4 record in the Grand Finals.

Dimitrov, seeded 9th, had played a five-setter in the fourth round and appeared to fade against Tiafoe late in the third set, clutching his left hamstring and walking cautiously between points. After that set, Dimitrov was visited by a trainer and then went to the locker room for treatment.

He returned to the court for the start of the fourth set, but could not move properly and eventually gave up.

The Fritz-Tiafoe semifinal — “That could be crazy,” Fritz said — is the first between two American men at a 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 2003 U.S. Open; Roddick was the last U.S. man to reach the U.S. Open final, losing to Roger Federer in 2006.

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

The Associated Press contributed to this report.