Cincinnati,  World No. 76, Switzerland's Jil Teichmann, who came back from a set down to defeat No. 2 Naomi Osaka and seal the biggest victory of her career at the Western & Southern Open, said that being an "underdog" she had to just "play my game," and wait for it to work.

Teichmann defeated Osaka 3-6, 6-3, 6-3 on Thursday evening to secure a quarterfinal berth in the Cincinnati tournament.

"I knew she's (Osaka) a very tough opponent. She's a Grand Slam champion. I'm the underdog, so... my plan was to just play my game," the 24-year-old Teichmann said.

"I move very good; I change up everything I can -- directions, height, everything -- and I think she didn't really feel very comfortable about it, and I served very good."

From the 3-0 deficit, Teichmann nearly pulled level in the opener to gain the momentum.

"I started actually really bad, two breaks down. I did breaks on my own. I wasn't serving good. I was doing unforced errors. So when I sat down after first set I was, like, 'Okay, I started off bad, but I'm actually close.' I didn't really feel like she's much better than me today right now," Teichmann told wtatennis.com

"I took this confidence into the second set. I was like, 'Okay, let's serve out well, and I will get my chances,' and to break her and that's a little bit what happened."

Staring down a nearly identical deficit in the final set -- serving at 2-0, 0-30 -- Teichmann stopped Osaka's momentum in its tracks, winning four straight games. The Swiss took a lead she'd never relinquish, despite double-faulting on break point when leading 4-2.

"I thought she played really well. I thought in the first set I was doing everything I was supposed to do, and then in the second set I feel like, and also in the third set I felt like I was a bit too defensive maybe," Osaka said about the defeat.

"I felt like I learned a lot from this match today, and I felt that, if anything to take away from this, I tried my best throughout the entire match, so I can sleep at night."

The Swiss No.3, who came into this tournament just 1-4 since suffering an ankle injury at the Internationaux de Strasbourg in May that forced her out of the French Open, added, "Literally, I'm shaking right now. I'm very, very happy with this win. I've had a very tough year: I started very well and I've had many, many injuries. But I felt like I've had a good level and I'm happy it's working out now."

On her next opponent, compatriot and No. 10 Belinda Bencic, Teichmann said, "Belinda has been amazing, Olympics, as well as [winning a silver medal in doubles] with Viktorija [Golubic]. I'm very close to both of them. I was actually calling them right after the matches," Teichmann said. "I'm just like really, really happy for Swiss female tennis. We really need that. We are very good players, and we are showing it. It's perfect, actually. It has been perfect.

"It's gonna be tough. But either way I'm ready. I'm gonna just enjoy the match. Obviously I'm going to go [and want] to win, but for sure, it's going to be emotional either way."