CINCINNATI, Ohio (Kyodo) -- A day after booking their spots in the quarterfinals, Japan's Naomi Osaka and Yoshihito Nishioka both pulled out of the Western and Southern Open on Friday.
Osaka battled back after losing the first set 6-4 to American Sofia Kenin, to take the second 6-1 before taking a medical timeout and getting her left knee taped up. The injury forced her to retire midway through the second game of the third set.
The world No. 1 said that during her final serve she felt something strange unlike any of her previous injuries. She also cited her frustration at getting injured before the U.S. Open, where she is aiming to defend her title.
Nishioka, who defeated his injury-slowed compatriot Kei Nishikori in the second round on Wednesday, withdrew before his quarterfinal match against Belgian David Goffin due to illness.
"I got a lot of experience. I'll do my best again," the 23-year-old Nishioka said.
The U.S. Open, the final Grand Slam of the season, starts on Aug. 26 in New York.