Japanese qualifier Miyu Kato stunned Serbia's Aleksandra Krunic in straight sets on Friday to reach the semifinals of the Japan Women's Open.

Kato, the world No. 171 and the only local player left in the singles draw, was in total control at Ariake Tennis Forest Park, running out a 6-1, 6-3 winner in 72 minutes to reach the last four of a WTA Tour event for the first time.

Kato will face Croatian qualifier Jana Fett, who continued her remarkable run with a 6-3, 4-6, 6-3 win over China's Wang Qiang.

"I think the win today was a result of me being focused from start to finish, just like I was in my last game," said Kato, who shocked fourth-seeded Czech Kristyna Pliskova on Wednesday.

"I am really pleased to have made the semis for the first time but I can't just be satisfied with this and just have to turn my attention to my next match."

Kato took a 3-0 lead behind some solid groundstrokes and after breaking for a second time, took the first set when world No. 67 Krunic dumped her return into the net.

The 22-year-old from Kyoto broke again to take a 2-1 lead with a superb passing shot and continued to hold her own serve before a wayward return from her opponent handed her victory.

Krunic had sent 46-year-old Japanese former world No. 4 Kimiko Date into retirement with a 6-0, 6-0 drubbing in the first round.

Asked if revenge on Date's behalf was an extra source of motivations, Kato said with a laugh: "I probably should say yes but I wasn't thinking about that at all. Even so it was nice to beat the player that beat Date."

Krunic paid full credit to Kato for her win.

"She was very solid, pretty fast on her legs," the Russian-born 24-year-old said. "She is a tough opponent to play against because she always gets and extra ball back. Today I don't think I was fit enough to cope with the rhythm that she gave me."

"Overall I am happy with my week. I am pretty consistent with my results lately, but obviously the fatigue gets to me slowly and mentally I wasn't at my best today. It was tough for me to focus but credit to her because she pulled out a really nice match."

Earlier in the day, American Christina McHale moved a step closer to retaining her title with a 6-4, 6-1 win over Belgian third seed Elise Mertens.

After a tight first set, McHale took control in the second and raced into a 5-0 lead. Mertens pulled one game back, but McHale closed out the match with a sizzling backhand down the line.

McHale will next face Kazak qualifier Zarina Diyas, who came from a set down to beat eighth seed and compatriot Yulia Putintseva 4-6, 6-1, 6-3.

"I think the first set was definitely back and forth, and then I felt like once I won that first set, I relaxed a little more in the second," said McHale.

"I served better in the second set so was able to hold serve more. Even in the second set we had some tough games but I was able to pull them out."

McHale's only title win so far on the WTA Tour came here last year, when she rallied from a set down to beat Katerina Siniakova of the Czech Republic 3-6, 6-4, 6-4 in a rain-interrupted final.

"Definitely it (defending the title) is in the back of your mind a little bit, but I try and think of it as a new year and just try and play some good tennis here," said McHale. "I love playing here so I am just really happy to be back."

In doubles, Japan's Shuko Aoyama and Chinese partner Yang Zhaoxuan beat the Japanese-Czech top-seeded pair of Makoto Ninomiya and Renata Voracova 6-4, 6-3 to advance to the final.

They will face Australians Monique Adamczak and Storm Sanders, who beat Mertens and Turkey's Ipek Soylu 6-3, 4-6, 10-5.