NEW YORK -- Karolina Muchova came into the US Open ranked outside the Top 50, but on Thursday night, under the bright lights of Arthur Ashe Stadium, she reminded everyone she still has the tennis that took her to the final four 12 months ago. 

In a showdown that felt out of place so early in the tournament, Muchova unleashed her creative all-court game to knock out two-time champion Naomi Osaka 6-3, 7-6(5) and advance to the third round.

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Muchova will face Anastasia Potapova in the third round. Potapova upset Leylah Fernandez in three sets in the first round and defeated Varvara Lepchenko in the second round. 

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Here's our three big questions coming out of Muchova's win:

How did she engineer such a dominant win?

Osaka and Muchova had split their two previous meetings, but this was their first match on a hard court in over four years. As the match began, Osaka picked up right where she left off with her stunning 6-3, 6-2 offensive masterclass against No.10 Jelena Ostapenko in the first round. Her serve was firing and the former No.1 was patrolling the baseline with ease. 

Osaka earned the first break point of the match at 2-1 but put a tight inside-out forehand into the net. She earned a small chance to break in Muchova's next service game, building a 0-30 lead, but the Czech bravely slammed the door with four straight unreturnable serves, including two aces and held to 3-3.

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Having dodged Osaka's early advances, Muchova dialed in. She unleashed a successful "SABR," charging into the net after an aggressive return and stuck the volley to get to 30-30 on Osaka's serve. She earned her first break point on a stunning drop shot that froze Osaka at the baseline, and then converted on a netted backhand from the former No.1 to lead 4-3. 

The reversal was swift and stunning from the Czech, who finished the set with 12 winners to just four unforced errors. Osaka also struck just four unforced errors, but Muchova successfully held her to five winners.

"I was just really trying to be focused," Muchova said. "I know she's an amazing player and that I have to bring the A-game to have a chance. So I was just trying to be really focused on myself. I knew I have to serve good because her serve is really good. So I was just trying to be kind of locked in myself and focused out there."

"Then the energy and the big court and all that, it for sure helps me. I like that."

Muchova continued her momentum and came within a point from running off six consecutive games. But Osaka steeled herself to hold to 1-1 and slowly worked her way back into the match. At 4-4, Osaka broke to earn a chance to take the match into a deciding set, but squandered a 40-0 lead in an error-strewn game to hand back her advantage.

In the tiebreak, Muchova surged ahead to earn two match points and Osaka nearly saved them both. But in the face of Muchova's scrambling defense, Osaka sprayed a forehand drive wide to end the match. 

"I think during the pressure moments I got nervous," Osaka said, and I don't know if I just have to keep playing more matches and get used to that feeling, especially on a really big stage.

"Honestly, if I get past the disappointment, I feel pretty proud of myself to have gotten that many opportunities while still feeling like I could have played much better."

Where did this tennis from Muchova come from? 

Talent and ability have never been the question for Muchova, who reached a career-high PIF WTA Ranking of No.8 12 months ago. The main impediment to her game as been her body, which has rarely let her play a full injury-free season.

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Muchova shut down her season after her semifinal run to the US Open last year, which came months after her first Grand Slam final at Roland Garros, and underwent wrist surgery. She returned to the tour just two months ago during the grass season and made a Hologic WTA Tour final in just her third tournament back in Palermo. She lost to Zheng Qinwen, who would go on to win Olympic gold in Paris.

If there's one thing Muchova has proven over her career, it's her ability to bring her best on the biggest stages against the game's biggest names. Six of her 11 Top 10 wins have come at Grand Slams. She remains the only player to win a set off World No.1 Iga Swiatek in a French Open final.

What's next for Osaka?

This loss will sting for the two-time US Open champion, whose level has been far better than her No.88 ranking. She has repeatedly been on the cusp of a big result, most memorably her three-set loss to eventual champion Iga Swiatek at Roland Garros, a loss in which she held a match point. All that work over the last eight months, her constant schedule and willingness to put herself on the line week in and week out, was commendable and brave, and it was all to peak in New York. 

"Honestly I feel like I'm coming back from pregnancy, but also, it wasn't like in 2022 I was the best version of myself," Osaka said. "So in some way, I had to catch up to that, and then also I'm trying to pass it at the same time.

It wasn't the fairytale she wanted, but there were gains made at her favorite Slam. Her win over No.10 Ostapenko was her first Top 10 win in over four years. Her level in both matches was more than good enough against most, but she's still looking for her reliable ability to close out sets and matches. 

"It's been a little difficult because obviously I can only gauge how I'm doing by results. Like, I feel faster. I feel better, but I lost in the second round. So it's a little rough."

But it doesn't end here for Osaka. She has committed to playing a full schedule during the Asian Swing, where she has enjoyed great success in the past. She was a champion in Beijing and Tokyo and if she can set this loss behind her, she can end her comeback season on a high note.