NEW YORK, NY, USA - Yulia Putintseva scored her best US Open result over an in-form Aryna Sabalenka on Thursday, upsetting the No.9 seed, 6-3, 7-6(3) to reach the third round for the first time.

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Putintseva twice reached the quarterfinals at Roland Garros and stunned World No.1 Naomi Osaka in the first round of Wimbledon, but had only won two main draw matches at the USTA Billie Jean King National Tennis Center coming into this year's tournament, doubling that number this week after a one hour and 57 minute win over her good friend.

"Now I owe her two dinners, probably!" she laughed, answering Sabalenka's challenge from before the match. "Maybe even one for her whole team if she decides.

"We started talking to each other a little bit more at the beginning of this year. She's pretty funny, has a good sense of humor, and is a nice girl, and it's nice to talk to someone about something other than tennis. I offered to take her to dinner yesterday, but she said to wait until after the match, and we made a deal that the winner pays! It's good to have friends like this because some players can take things too close to heart."

Sabalenka was fresh off an encouraging win over countrywoman and two-time US Open finalist Victoria Azarenka, and enjoyed a strong start to her afternoon encounter with Putintseva on Court 7, breaking first for a 3-1 lead.

"I was expecting a tough battle out there, because I know how great Aryna is playing when she's on. I was just preparing to get ready for some big shots, and for the big angles, and do what I can in big moments. I couldn't just get the ball back, but I had to be aggressive and do my best."

The Belarusian soon struggled with her range as Putintseva played far more consistently to sweep the next five games and take the opening set.

Sabalenka soon steadied to edge ahead 5-3 in the second, holding a set point in the following game. Putintseva ultimately leveled proceedings and forced a tie-break.

"At this point, I always say that a tie-break is like a lottery, and there's a 50-50 chance because you never know who is going to make it. Especially with Aryna, who can make winner after winner, you can't do anything with that, so you have to accept that, play each and every ball, and do anything I can."

Rallying from another deficit in the ensuing Sudden Death, the Kazakh rolled off six straight points to earn her first match point. One last backhand error from Sabalenka put Putintseva over the service line and into the third round.

"In the end I was able to stay focused, play some good rallies, and I won them. That's what made the difference, just a few points here or there."

In all, Putintseva was far too consistent for Sabalenka, striking an even 10 winners to 13 unforced errors, while the latter hit 31 winners but also 51 unforced errors. 

Standing between the unseeded 24-year-old and the second week will be No.22 seed Donna Vekic, who ousted two-time quarterfinalist Kaia Kanepi in straight sets.

"It'll be another tough battle and another big hitter, and I'll have to prepare again with the right mindset, and just get ready."