NEW YORK >> For two full sets, Alexander Zverev was confused and listless, his body language as poor as his winner-to-error ratio against Pablo Carreño Busta in the U.S. Open semifinals Friday.

Zverev double-faulted and smacked his left high. He put a backhand into the net to cede the opening set and covered his face with both hands. He netted a forehand early in the next set — part of a stretch in which he dropped nine points in a row and 17 of 19 — then turned a forlorn face toward his guest box and put his palms up.

When he pushed a backhand long after 1 hour, 25 minutes of play and shook his head, Zverev trailed by two sets, a deficit the 23-year-old German never had overcome. Never had been to a Grand Slam final, either.

Done and done.

Zverev constructed quite a comeback, getting his game in gear to beat a fading Carreño Busta 3-6, 2-6, 6-3, 6-4, 6-3 and reach the title match at Flushing Meadows.

“Mentally, I stayed in it. … A lot of players would have gone away,” Zverev said. “There’s no easy matches anymore. Sometimes you have to dig deep. Today I dug deep, dug very deep.”

Zverev is the first man to win a U.S. Open semifinal after a 2-0 set deficit since Novak Djokovic did it against Roger Federer in 2011 — and, keeping good company, he’s also the youngest male finalist at any major tournament since Djokovic was 23 in New York in 2010.

Zverev, the No. 5 seed, will play No. 2 Dominic Thiem for the championship today. Thiem was a straight-set winner over Daniil Medvedev 6-2, 7-6 (7), 7-6 (5).

It had been 16 years since Grand Slam semifinals were held without Federer, Djokovic or Rafael Nadal involved.

Nadal chose not to try to defend his title in New York because of the coronavirus pandemic; Federer is out for the rest of 2020 after two knee operations; Djokovic’s tournament ended at 6-5 in the first set of his fourth-round match against Carreño Busta when the No. 1 seed and title favorite unintentionally hit a line judge in the throat with a ball after getting broken.

None of the semifinalists owns a Grand Slam trophy yet.

Zverev has been considered likely to grab one, given his success at other events and all of the talent in his 6-foot-6 (1.98-meter) frame.

His first trip to a major semifinal came in January at the Australian Open, where he was eliminated by Thiem.

Now he’s gone a step further.

A day after a pair of well-played and competitive women’s semifinals — won by Naomi Osaka and Victoria Azarenka, who face each other today for the championship — Carreño Busta vs. Zverev offered little in the way of those characteristics for two sets.

“A big opportunity,” Carreño Busta called it.

Before the start of the fifth set, Carreño Busta took a medical timeout and got his back worked on by a trainer, something he did at the same stage of his marathon quarterfinal victory over Denis Shapovalov.

This time, it was Zverev’s surge that continued, undeterred when Carreño Busta twice hit balls right at him during points in the fourth set.

When it ended with one last break of serve, Zverev finally could throw his head back and allow himself a wide smile.