Zheng's compatriot Li Na followed her into the quarterfinals on Monday after stunning fourth-seeded Dane Caroline Wozniacki in straight sets.

CNN: Tennis: Henin battles into semis

Latvia's Gulbis, seeded 24th, lost in straight sets to Jeremy Chardy , 28th seed Radek Stepanek lost 6-4 6-2 4-6 6-4 to Julien Benneteau and 30th seed Juan Monaco was sent packing by Canada's Peter Polansky in straight sets.

BBC: Rafael Nadal beats Teymuraz Gabashvili at the US Open

In the early matches, fifth-seeded Amelie Mauresmo eliminated Russian Tatiana Panova in straight sets 6-4 6-3.

BBC: Johansson crashes out in Moscow