NEW YORK, NY, USA - Having waited 11 years to reach one milestone, Kristie Ahn is making up for lost time by smashing through a new one every time she takes the court at the US Open this year.

The American made her Grand Slam debut here as a 16-year-old qualifier in 2008 - but it was a decade before she would make her second appearance in the main draw of a major, at the Australian Open last year, and her 11-year-gap between her main draw debut and her first main draw win this week is an Open Era record. But after upsetting 2004 champion Svetlana Kuznetsova in the first round, Ahn has kept going - and going. A defeat of qualifier Anna Kalinskaya put the wildcard into the third round - and yesterday a 6-3, 7-5 upset of 2017 Roland Garros champion Jelena Ostapenko, her second victory over the Latvian this year, means that Ahn will make her major second-week debut.

Read more: Kristie Ahn comes full circle at US Open: 'I'm going to try and milk this as long as I can'

"If I don't fully process it, then I'll never have to fully deal with it," the 27-year-old, whose pursuit of a tennis career has required her to persuade her reluctant parents of its merits above a corporate office job, smiled afterwards. "When I go back to the hotel, I just think about how awesome of an opportunity it is and what a great experience it's been this week. Nobody can take that away from me. So I'm just so happy about it."

After coming through a tight second set to seize her first match point with an ace, Ahn let all her pent-up emotion out in an unbridled celebration - part joy, part disbelief. "[World No.168] Ellen Perez on Twitter was like, You add a second to your celebration every win," revealed Ahn. "She was expecting a three-second celebration. I tried to make it a little more dramatic. No, I'm just kidding - it was exciting, because I hit an ace, which I never do. 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.' But all my friends told me they cried too, so I guess that's OK!"

The relief was also partly due to putting away an unpredictable opponent with the potential to hit a hot streak at any time. Ahn had beaten Ostapenko once before, in the first round of Bogota in April - but that match had been a rollercoaster ride in which she had come back from 2-6, 0-3 down but lost a break lead in the final set, before saving two match points to capture a 2-6, 7-6(5), 7-5 victory on her own fourth match point. Moreover, that contest had come one week after former World No.5 Ostapenko had saved a match point herself en route to overturning a 1-5 final set deficit to beat Shelby Rogers 4-6, 6-3, 7-6(4) in Charleston.

"She's come back from pretty much every score possible probably, so I was really keen on getting first match point done," laughed Ahn.

The World No.141, who won the USTA's US Open Wildcard Race to seal her main draw berth - in lage part due to a quarterfinal run as a qualifier in San Jose - attributes her success this year to experience and a good team around her. "Since Wimbledon, I've been able to accumulate a lot of little life chips, little wins," she explained. "We call it stacking up the wins. Even if you lose a match, what you're able to take away are the positives, and being able to just keep that building. One day you'll be able to have little towers.

"I feel like that's what I've been able to really hold onto this week is in those tough moments I know that I've been playing really good tennis. And the tennis that I've been playing, I'm not just training out of my mind, I've backed it up. That's even a better feeling... 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. And I feel like that's what's really been stacking me these past couple weeks."

The size of her towers now? "It's like the Empire State Building," smiled Ahn.