"It feels great, but it's still not like I won the tournament," she told press after the match. "It's only the second round."
The Latvian had reached a career-high ranking of No.36 back in 2011 before a series of injuries led her into early retirement in 2013.
"Again?" a smirking Sevastova asked when encouraged to retell her inspiring origin story. "I stopped playing in 2013. I had many injuries, and I wasn't happy with my tennis or where I stood on the tennis court. Something different was hurting all the time: back, arm, and legs. Then I decided to go out and retire.
"I did some studying. I coached some kids, but nothing serious. Just lessons, and lived a normal life. I studied management. It was strange," she trailed off as a wry grin returned to her face. "I didn't find it that difficult to study, but maybe it made me go back to tennis."
For one playing the smallest of ITF Challenger tournaments just under two years ago, the gravity of the moment seems largely lost on Sevastova, at least until the perspective retirement gave her shines through.
"I've seen that there's life after tennis, that if you lose a match, it's not the end of the world. The world does not collapse."
And yet it so often does for players who've pulled off massive upsets; the pressure to prove their win wasn't a fluke can leave them frozen in place. From the night match on Arthur Ashe Stadium, Sevastova was sent out to Court 17 in broad daylight to take on Kateryna Bondarenko, a 2009 quarterfinalist who'd won all three of their previous matches in straight sets.
"It was different conditions, and a completely different match - the first match on," she said in Friday's post-match press conference, wearing a New York Yankees cap. "In the beginning, I didn't manage it that well. The court was a bit faster, and it wasn't night match, so it was different.
"In the warm-up, I felt good, but in the first games, I wasn't putting anything in. Maybe it was the expectations, but I kept fighting, stayed positive, and made it through the tough games at 4-3 and 5-4. It was important to win the first set, for sure."
Sevastova recovered from an early break to win 12 of the final 14 games to book a spot in the fourth round, her first anywhere since her 2011 breakthrough at the Australian Open, and her first in Flushing Meadows.
"They always say it's tough after a big win to back it up. But I don't know what happened in the beginning. I was a little too nervous. But it was strange."
Strange, but not impossible as she prepares to play No.13 seed Johanna Konta for a spot in the quarterfinals.
"In women's tennis, it's possible; anyone can beat anyone on a good day. On a bad day, you can lose to anyone! But I think Jo has had a good year, very stable. She's one of the best players, Top 15. She serves well and has no weaknesses.
"It's not an easy match, but then, it's the round of 16 at the US Open," she clarified as a smile returned to her face. "It's not the 10K in Sharm El-Sheikh."
Far from where she kickstarted her career, Sevastova remains unfazed by fame, even as her star rises here and at home.
"There was one headline, where they posted something like, 'Look Into Anastasija Sevastova's Private Life,' and they posted Instagram pictures. It's funny. Maybe they don't have anything else to write about in Latvia, but they need some positive news!
"Sometimes people know me in my hometown, but if I go to Riga, I don't think they'll know me. I'm probably D-list," she deadpanned.
Just shy of matching that initial career-high rank, Sevastova will likely leave New York somewhere in between Kathy Griffin and Nicole Kidman, but with plenty of room to grow with the help of that mature mindset.
"Tomorrow is a new day. There are other matches. Nobody thinks about the previous match. You have to think forward. But tonight, I can enjoy."
All photos courtesy of Getty Images.