GUANGZHOU (AFP) - Four of the top five seeds, including No. 1 pick Samantha Stosur, crashed out of the US$500,000 (S$631,900) WTA Guangzhou Open in the first round Tuesday, as the former US Open champion's poor run of form continued.

Australian Stosur lost to home wildcard entry Wang Yafan 2-6, 6-2, 6-2, making seven double faults in a two-hour, three minute match.

On a day of shocks, fourth seed Bojana Jovanovski of Serbia lost to Romanian Monica Niculescu 6-2, 6-2, while Zarina Diyas of Kazakhstan, seeded five, crashed out to Hong Kong's Zhang Ling 6-4, 6-1.

Third seed Sloane Stephens of the United States lost 6-3, 4-6, 6-4 to Spain's Silvia Soler-Espinosa in the day's last match.

Stosur won the US Open in 2011, a season which saw her climb to No. 4 in the world rankings. But she is now at 20 after failing to get past the semi-finals of any of the 18 tournament she has competed in so far this year.