Four-time major winner Naomi Osaka has been knocked out of the Pan Pacific Open by 18-year-old Mia Pohankova of Slovakia

TOKYO -- Four-time major winner Naomi Osaka lost in front of her home crowd to Slovakian teenager Mia Pohankova in the Pan Pacific Open round of 16 on Thursday.

Pohankova, who turned 18 a week ago and was a wild card entry, upset No. 7-seeded Osaka 6-3, 7-5 to advance to the quarterfinals.

Pohankova will face Alycia Parks next. Pohankova was the 2025 junior singles champion at Wimbledon.

Osaka was coming off a win over Jasmine Paolini in the first round in Tokyo.

In other round-of-16 matches, top-ranked Elena Rybakina beat Yulia Putintseva 6-2, 6-3 and Leylah Fernandez defeated No. 14 Elise Mertens 6-2, 7-6 (8).

Second-seeded Maja Chwalinska and No. 4 Belinda Bencic pulled out of the tournament earlier with injuries. Chwalinska had an injured left thigh and Bencic had a right-ankle injury.