Former number one and fourth seed Karolina Pliskova became the latest high-profile casualty at the China Open on Thursday, going out in the third round to unseeded Sorana Cirstea.
Cirstea follows fellow Romanian Simona Halep into the quarter-finals after the second seed sent Maria Sharapova packing on Wednesday.
Cirstea, ranked 44 in the world, stunned the Czech Pliskova 6-1, 7-5 on Beijing's outdoor hard courts to surge into the last eight.
She will play Latvia's Jelena Ostapenko, the Roland Garros champion, after China's top player Peng Shuai retired with a knee injury at 3-0 down in the first set.
The 31-year-old Peng said she had been having injections to ease the pain and her right knee was heavily strapped, but she could not play on.
"The doctor suggested I should take a period of rest and get it treated, but I can only rest after the season, that's the plan," said Peng, ranked 25 in the world.
World number one Garbine Muguruza and reigning champion Agnieszka Radwanska are both out to leave world number two Halep the favourite in the Chinese capital.
Also into the quarters are Caroline Garcia, who defeated French compatriot Alize Cornet 6-2, 6-1, and Barbora Strycova of the Czech Republic.
Garcia is in red-hot form after winning the Wuhan Open title on Saturday.
In the men's draw the American John Isner blasted his way into the last eight with a 6-0, 6-3 beating of Argentina's Leonardo Mayer.