Wildcard Jil Teichmann scored the biggest win of her career on Thursday night at the Western & Southern Open, knocking out defending finalist and No.2 seed Naomi Osaka from a set down, 3-6, 6-3, 6-3. 

Osaka sprinted out to a 3-0 lead in the opener, but the Swiss was more than in the match from that point on: using her natural athleticism and defensive skills, Teichmann lured Osaka into lengthy rally after lengthy rally, increasingly frustrating the four-time Grand Slam champion with her dogged determination and variation of spins and slices.

After the match, the world No.76 revealed that was her intention.

"I knew she's a very tough opponent. She's a Grand Slam champion. I'm the underdog, so... my plan was to just play my game," Teichmann said in her on-court interview.

"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: Osaka saved a break point for 4-4 en route to taking a one-set leadt. The Swiss' momentum was already established, though, and from 6-3, 2-1 down, she won five of the next six games to force a decider.

"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 added in her post-match press conference.

"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, Teichmann 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 in 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."

Stats of the Match: The loss is just Osaka's fourth after winning the first set since 2017, a record which was 118-3. It is also Teichmann's third career Top 10 win, but first on hardcourts. Her prior wins over Kiki Bertens, to win the title in Palermo in 2019, and Elina Svitolina, earlier this year in Madrid, came on clay.

Teichmann hit more aces than Osaka (8 to 6) and more winners (21 to 17), while Osaka racked up 41 unforced errors to Teichmann's 29. In addition, Teichmann went 6-for-12 on break point chances against Osaka's vaunted serve.

The Swiss No.3 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, but beat Sorana Cirstea and Bernarda Pera with the loss of just eight games combined to advance to this round. She also had previously missed five weeks between Miami and Madrid with another injury.

"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."

- Jil Teichmann

Up next for Teichmann for a place in the biggest semifinal of her career will be her compatriot, No.10 seed Belinda Bencic, who advanced to the quarterfinals when Karolina Muchova retired due to injury trailing 7-5, 2-1. 

"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."