BEIJING - China's Zhang Shuai beat former world No 1 Naomi Osaka of Japan 6-4, 7-5 in the first round of the Western & Southern Open in Cincinnati on Tuesday.

Four-time Grand Slam Champion Osaka struggled with only 53 percent accuracy on her first serves and 29 unforced errors, while Zhang had an 85 percent first-serve percentage.

Osaka, who retired from her opening match at National Bank Open last week due to injury, has been eliminated from the first round of two consecutive WTA 1000 Opens.

"She's my friend and I've known her for many years. It was tough for us on the court and we didn't fully release our emotions. Even so, we were very focused on every point," said Zhang.

Zhang leveled their head-to-head record at 3-3 after this win. She will now meet Ekaterina Alexandrova of Russia.

Elsewhere, Zhang's compatriot Wang Xinyu ended her five straight losses after defeating Kristina Mladenovic of France 6-4, 6-2 at the Odlum Brown VanOpen.