Naomi Osaka makes 2nd straight early exit at Cincinnati Open

Naomi Osaka's U.S. Open preparations suffered another setback when the former world No. 1 was swept aside 6-4, 7-5 by China's Zhang Shuai in the Cincinnati Open first round on Tuesday.

It was only Osaka's third tournament back from an Achilles injury and it has been a stuttering return to action for the twice U.S. Open champion, who also exited in the opening round in Toronto last week, retiring with lower back pain.

For Zhang, doubles champion in Cincinnati last year, it was her first singles win at the event since 2014.

The first match on Centre Court, Japan's Osaka got the contest off to a sluggish start by double-faulting to gift Zhang a break on her opening serve.

That was all the help Zhang needed as she went on to take the first set with the 33-year-old Chinese player then quickly gaining the upper hand in the second with an early break to go ahead 2-1 as Osaka continued to misfire.

With Zhang serving for the match at 5-4, Osaka finally secured an elusive break to level the set only for her opponent to immediately break back and regain control.

Osaka at work