Second seed Danka Kovinic was knocked out of the Dalian Women's Open on Thursday, while top seed Duan Ying-ying saved a match point before battling through to the quarter-finals.
Vitalia Diatchenko recorded a 6-3 2-6 6-3 victory over Kovinic, who was hampered by nine double faults as she made an early exit in China.
Duan was required to pull off a superb fightback in order to maintain her perfect record against Liu Fangzhou.
After trailing 3-1 in the second set, Duan faced match point in a tie-break, but ultimately prevailed 5-7 7-6 (10-8) 6-4.
Vera Zvonareva was also among the second-round winners, beating Gao Xinyu 6-4 6-4. Zvonareva and Diatchenko are both in the bottom half of the draw, which has been shorn of seeds.
In the top half, Duan was joined in reaching the last eight by fellow seeds Kateryna Kozlova, Zarina Diyas and Han Xinyun.