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.
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.
In other second-round matches, Italy's Roberta Vinci beat Irina Begu 2-6, 6-4, 6-1 while Alize Cornet shocked Daniela Hantuchova 6-3, 6-3.