MADRID, Spain - Kateryna Kozlova is making the most of her Mutua Madrid Open debut, matching her career-best Premier Mandatory result with a 7-5, 2-6, 6-4 win over former World No.1 Karolina Pliskova to reach the Round of 16 at the Caja Magica.

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"I was pretty consistent in the points, and when I could handle her serve, I was playing smarter in the rallies," she explained after the match. "I was able to stay strong on my serve, which is never easy against Karolina and her huge, fast serve. That can sometimes make you feel more pressure on your own serve, and I don't think I handled it great in the third set, but eventually I'm glad I could handle my nerves in the last game."

Kozlova recently reached the third round of the BNP Paribas Open - where she fell to reigning Roland Garros champion Simona Halep - and scored her second Top 5 win over Pliskova after one hour and 51 minutes on Court Arantxa Sánchez.

"This win means a lot because it's always an amazing feeling to beat someone that good. It gives you confidence, and I think we're all working so hard to play at their level, so when you get the win, you feel like, this is why I'm here.

"I didn't have ranking goals - though you always want to get better in the rankings - but I wanted to play more matches, especially against top players, so I could get more experience. I wanted to keep thinking about my game, get better every day, and learn from every match."

Ranked World No.85 coming ahead of her Madrid debut, Kozlova stunned 2017 French Open champion Jelena Ostapenko in the first match of her title defense last spring, showing a definite clay court prowess that was on display early on against Pliskova, trading routine service holds before getting the first break of the match.

"She serves so well, that when she does miss a first serve, you feel relieved, but I had to take my chance on every second serve, either by playing more aggressively or deep to get into the rally. That was just my mentality."

Though Pliskova broke straight back, she lost serve again in the 11th game, allowing the Ukrainian to serve out the opening set.

Cutting down on her unforced errors - hitting 18 in the first set alone - Pliskova regrouped to level the match in style, breaking serve behind a stirring lob volley winner and managing a second break to force a deciding set.

The final set followed a similar pattern to the first; Kozlova and Pliskova exchanged breaks in the middle of the set. The three-time WTA Ace Leader seemingly with the momentum as she held for 4-3, but it was Kozlova who remained nerveless throughout, gamely holding serve to pressure the Czech powerhouse, breaking once more and securing the upset to love.

"I was thinking how, in the last two months, I've been playing pretty good. I played a close match against Simona in Indian Wells and another against Aryna [Sabalenka] in Charleston. Those are great opponents, so I felt like I had a good level because I could compete with them.

"I was just trying to remind myself that I'm playing well and not to doubt, do my best, and see what happens. I can't say I expected to win, just that I was coming on court to do my best and fight until the last point. In the tough moments, I was reminding myself to stay strong!"

Standing between the unseeded Ukrainian and her first Premier Mandatory quarterfinal is former World No.7 and reigning Dubai Duty Free Tennis Championships winner Belinda Bencic, who outlasted a thrilling challenge from two-time Grand Slam champion Svetlana Kuznetsova late Monday night.

Friends with both Kozlova and Pliskova, Bencic was seen in the crowd watching the match alongside father Ivan.

"I don't remember how we got to know each other exactly; she's a little bit younger, so we didn't play juniors together. When she practiced in Slovakia, we started to become friends, and we played doubles in Paris and London last year. We were feeling good playing with each other, and off the court, she's a very nice girl. We've continued having good relations, so I'm glad we can share the court in singles, even against each other.

"She's having an amazing season, so it'll be another tough match for me and another top player. The challenge is in playing against such good players, but I like to play in big stadiums. I remember my first match like this didn't go so well, but I got used to it, and now I really enjoy the crowds. It's an unbelievable feeling, and you also don't feel the same pressure because you can't expect to win. It's more about going for it and showing your best tennis."