Sebastian Korda becomes first seeded American man to fall at US Open in second-round upset

This happens year after year, at Grand Slam after Grand Slam, until years become decades and the championship drought — now 21 years — ages another year.

It always starts with one American losing in the men’s draw. It has always ended with the rest of them falling.

And on Thursday, at Louis Armstrong Stadium, it was Sebastian Korda — seeded No. 16 but the fourth-highest American in the U.S. Open bracket — who revealed the first crack in the quest to win that elusive title, with unseeded Tomas Machac winning 6-4, 6-2, 6-4 during their second-round match.

Korda was hampered by an elbow injury that bothered him for a week, and he never truly recovered after dropping the final four games of the opening set en route to becoming the first seeded American eliminated from the men’s draw.

American Ashlyn Krueger notches another impressive US Open upset

“I’ve never had any elbow issues before,” Korda said. “Every time I kind of overextend it, it bothers me pretty much. My serve today was a pretty perfect image of how I’m feeling and, yeah, just wasn’t good today.”

Korda snagged a 4-2 lead in the first set and served for a three-game lead, but after taking a 40-0 advantage, Machac took the next three points.

Machac missed his first chance to break, but when Korda’s shot in a lengthy rally landed just beyond the baseline, Machac pulled within a game. He didn’t lose the rest of the set.

Korda’s elbow — and the serves it prevented him from executing — was at the crux of what went wrong for him.

Aaron Judge, Anthony Rizzo take in US Open action with their wives on Yankees’ night off

He doesn’t know the type of injury, but in the second set, he took a medical timeout. Korda wanted tape to stiffen the elbow up, he said, because he didn’t want to overextend it and cause more pain.

“Helped a little bit,” he said, “but definitely didn’t solve it.”

Still, Korda jumped out to a 3-0 lead to start the third set. There was a fist pump. His shots were crisp. It was a flash of the potential that sparked his rise up the rankings in the first place.

CLICK HERE TO SIGN UP FOR OUR STARTING LINEUP NEWSLETTER

When Machac faced a break point down 4-3, though, he ripped off a 118 mph serve and eventually salvaged the game. Then, he won the next two games and threw his arms into the air after advancing.

“Just no serve today,” Korda said. “When you’re not serving, it’s pretty tough to really do any damage.”

Korda still is just 24 years old. He’s a key piece of the future core in American tennis, along with the other four — Taylor Fritz, Ben Shelton, Tommy Paul and Frances Tiafoe — in the ATP top 20.

But Korda has advanced to the quarterfinals of a Grand Slam just once. He had a brutal exit in the first round of Wimbledon last month.

He now has the elbow injury to navigate, too.

And in the present, in the overarching context of the drought, the collection of players with a shot to prevent 21 from eventually becoming 22 has thinned again.

For the latest in sports, top headlines, breaking news and more, visit nypost.com/sports/