Caroline Wozniacki of Denmark hits a return to Christina McHale of US during their second round match of the Cincinnati Open tennis tournament in Cincinnati, Ohio, August 17, 2011. World number one Caroline Wozniacki suffered a shock second-round loss to 19-year-old American Christina McHale at the Cincinnati Open on Wednesday. [Photo/Agencies]

MASON, Ohio - World number one Caroline Wozniacki suffered a shock second-round loss to 19-year-old American Christina McHale at the Cincinnati Open on Wednesday.

With golf sensation and friend Rory McIlroy in attendance, the Danish top seed never looked close to her best and lacked winning shots as she fell 6-4 7-5 to the 76th ranked McHale.

The defeat was the first time Wozniacki lost to an opponent outside the top 75 since 2009 and extends a worrying spell of form for the Dane.

Wozniacki, who suffered early round exits in her last two tournaments, handed victory to McHale with an awfully-timed stroke which looped way over the baseline.

The 21-year-old heads to the US Open later this month in search of her first grand slam title.