Big-serving Ben Shelton overpowered US compatriot Frances Tiafoe in four sets on Friday to reach the first Grand Slam final of his career, booking a US Open title showdown with Alexander Zverev.

Eighth-seeded Shelton blasted 20 aces on his way to a thrilling 4-6, 6-3, 6-3, 7-5 victory on the Arthur Ashe Stadium court.

Top seed Zverev held off 50th-ranked Russian Karen Khachanov 6-3, 7-6 (9/7), 7-6 (8/6) to reach his third straight Grand Slam final -- a run that delivered his maiden major at the French Open and saw him finish runner-up at Wimbledon.

Shelton -- who took down defending champion Carlos Alcaraz in the quarter-finals -- will now have the chance to become the first American man to win a Grand Slam title since 2003, when Andy Roddick triumphed at the US Open.

"It's a lot of emotion," Shelton said in an on-court interview. "My dad, my mom have sacrificed a lot for me to be in this position today. My dad lost his mom earlier this year, and she's the reason that he was able to play tennis.

"Without her, there's no Ben Shelton standing here today. So this one is for her. And I'm gonna need you guys on Sunday to bring the energy. I'm going for it. I'm gonna leave it all on the court."

Zverev is eager for the chance to play spoiler.

"Hopefully I can not make the American dream come true on Sunday," the German said.

The pulsating all-American semi-final played out in front of a star-studded crowd, with tennis legends including Serena Williams, Stan Smith and Lindsey Davenport on hand along with actors Ben Stiller and Rami Malek and New York Knicks star Jalen Brunson.

Tiafoe claimed the first set after Shelton uncharacteristically double-faulted to trail at 5-4.

They traded breaks early in the second, but Shelton took advantage of Tiafoe's increasingly erratic serve to break for a 5-3 lead and level the match.

The momentum was all with Shelton, who broke for a 3-2 lead then seized the set with a break in a marathon ninth game that went to deuce seven times.

The tension was mounting in the fourth set, but Shelton kept his composure as Tiafoe raised his level and gained the crucial break in the final game.

On Sunday he'll be up against an experienced opponent in Zverev, who after laboring through two five-setters to open the tournament has steadily upped his game.

- 'Anything but straightforward' -

Zverev doused Khachanov's hopes of reaching a first Grand Slam final, although the Russian -- who fell to Zverev in the Olympic gold medal match in Tokyo in 2021 -- put up a spirited challenge in the second and third sets.

"Straight-set win, but anything but straightforward," Zverev said. "He played incredibly well, fought incredibly well."

Khachanov denied Zverev on two set points in the second set tiebreaker  with a thumping forehand and a brilliant backhand down the line before Zverev closed out the set.

Neither player mustered a break point in a tense third set. But when Khachanov took a 6-4 lead in the tiebreaker he surrendered both set points with forehand errors. Zverev came up with his 15th ace and sealed the win when Khachanov sent a forehand long.

"Second and third set I think it's more than obvious that they could have gone both ways," Zverev said. "I just played a few points better here and there."

A somber note was struck during the national anthem ceremonies of both the day and night sessions on the 25th anniversary of the September 11 attacks that brought down the twin towers of the World Trade Center in New York.

"It's a difficult day to be out here playing," Shelton said in his remarks to the crowd. "My thought and payers go out to all the families affected by 9/11."

The women's final is on Saturday, when Kazakhstan's Elena Rybakina will try to deny Aryna Sabalenka a third straight title just days after ending the Belarusian's near two-year reign atop the world rankings by reaching the semi-finals.