Naomi Osaka battled through injury and her emotions to reach the quarter-finals of the Japan Open on Wednesday, choking back tears after hitting the winning shot against defending champion Suzan Lamens.

Top seed Osaka, playing a singles tournament in her native Japan for the first time in three years, won 7-6 (8/6), 3-6, 6-2 to set up a last-eight match against Romania's Jaqueline Cristian.

"Emotionally I was going through a lot in this match," said Osaka.

"And then in the third set I tried my best to have no regrets."

The former world number one was leading 5-0 in the final set in the city of Osaka when she needed a medical timeout to receive treatment on her left leg.

She returned with heavy strapping on her thigh and lost the next two games before closing out the match in 2 hours, 20 minutes.

Four-time Grand Slam champion Osaka hit a backhand winner and then bent over and put her hand to her face before walking to the net appearing to fight back tears.

Osaka said she had taken painkillers but admitted that her injury "doesn't feel good".

"I couldn't really move that well," she said.

"It's not good, but I think I'm a fast healer so it should be OK for my next match."

The 27-year-old is playing in her first tournament since reaching the US Open semi-finals, where she lost to Amanda Anisimova of the United States.

Osaka had not progressed to the second week of a major since winning the Australian Open for a second time in 2021.

She is now ranked 16 in the world.