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 last week and was a wild-card entry, upset No. 7-seeded Osaka 6-3, 7-5 to advance to the quarterfinals. Pohankova, the 2025 junior singles champion at Wimbledon, will face Alycia Parks next.
Osaka was coming off a win over Jasmine Paolini in the first round.
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.