Kristie Ahn, winless in three Grand Slam matches entering the US Open, was in tears Saturday after ousting her second Slam winner of the week to reach the fourth round.

The 27-year-old American of Korean descent fired a final ace to defeat Latvia’s Jelena Ostapenko 6-3, 7-5, the 2017 French Open winner making 45 unforced errors to join 2004 US Open winner Svetlana Kuznetsova on Ahn’s victims list.

“It was exciting because I hit an ace, which I never do,” Ahn said. “I could finally let my emotions get to me. The crowd roared. It was such a cool environment.

“When I looked back, I was like, ‘You cried, what a little baby.’ All my friends told me they cried, too, so I guess that’s OK.”

The 141st-ranked wildcard will play for a quarter-final berth on Monday against Belgian 25th seed Elise Mertens.

Ahn is feeling confidence to rival the most famous of Manhattan’s skyscrapers after a season of learning.

“I’ve been able to accumulate a lot of little life chips, like little wins,” Ahn said. “Even if you lose a match, what you’re able to take away, the positives, and being able to just keep that building, one day you’ll be able to have little towers.

“It’s like the Empire State Building now.”

Ahn says she isn’t really doing anything different than she had before.

“I feel like the tennis has been the same but it’s just the ability to mentally dig in a little bit deeper in those tough moments,” Ahn said. “I’m just really proud of how I was able to stay mentally focused and not let the nerves get the best of me.”

Ahn entered her match with her right elbow taped and left with her right knee taped as well after skidding to a sudden stop in the second set.

The latest injury came the same day Don Ahn, Kristie’s dad, told the New York Times about his concerns with a tennis career, saying: “If you get injured you’ve got nothing. There’s no employment compensation. You just get hungry, and without money.”

While the knee is sore, Ahn expects to be ready for Mertens. Until then, she’s going to keep enjoying the fairy-tale run.

“When I go back to the hotel, I just think about how awesome of an opportunity it is and what a great experience it has been this week,” she said. “I’m just so happy about it.”