Peng Shuai of China celebrates after defeating Agnieszka Radwanska of Poland during their match at the 2014 US Open tennis tournament in New York, August 27, 2014.[Photo/Agencies]

Peng Shuai of China upset fourth-seeded Agnieszka Radwanska of Poland 6-3 6-4 in a shocking start to the women's second round of the US Open on Wednesday.

The 28-year-old Peng, the doubles world number one, used her piercing, two-fisted groundstrokes to put Radwanska on the defensive and claimed the biggest scalp of the championship on her third match point with a backhand crosscourt winner.

Peng, the French Open doubles champion who is looking for her first career WTA Tour title, registered 28 winners in the 96-minute match.

The unseeded Chinese, ranked 39th in singles, will play either 28th seed Roberta Vinci of Italy or Irina-Camelia Begu of Romania in the third round of the year's final grand slam.