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

With golf sensation and rumoured new boyfriend 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.

Serbian Ana Ivanovic's disappointing season continued with a 6-3 7-6 loss to Russia's Nadia Petrova, but another Serbian former number one, Jelena Jankovic enjoyed a 4-6 6-3 6-1 win over China's Zheng Jie.

Germany's Andrea Petkovic advanced with a 6-2 6-4 win against Sweden's Sofia Arvidsson.

Reuters