DALIAN, China - Unseeded Vitalia Diatchenko scored the best win of her comeback this year with a 6-3, 2-6, 6-3 victory over No.2 seed Danka Kovinic to move into the Dalian Open quarterfinals.

The World No.250, who reached a career high of No.71 in 2014, entered the WTA 125K event with a 11-2 record in her previous three ITF events. Diatchenko extended her fine form by slamming down three aces and reeling off the final eight points to move into the quarterfinals, while her Montenegrin opponent was undone by nine double faults.

27-year-old Diatchenko wasn't the only returning Russian making waves on Thursday. Former World No.2 Vera Zvonareva, having upset No.3 seed Chang Kai-Chen in the first round, backed that win up with a more straightforward 6-4, 6-4 victory over Chinese 19-year-old Gao Xinyu today. Both sets began with an exchange of breaks before the 32-year-old Russian captured the crucial break of Gao's serve to love in the fifth game of each.

The tournament came within a point of losing its top two seeds on Thursday - but while Kovinic fell to her resurgent opponent, No.1 Duan Ying-Ying survived a match point in an epic second-set tiebreak to overcome compatriot Liu Fangzhou 5-7, 7-6(8), 6-4 for the fifth time in as many meetings. The 28-year-old had also trailed 1-3 in the second set before making her comeback.

Elsewhere, No.3 seed Zarina Diyas made smooth progress over 17-year-old qualifier Wang Meiling 6-1, 6-3 and No.6 seed Han Xinyun edged Lu Jing-Jing in an all-Chinese affair 6-3, 1-6, 6-3 to seal an all-seeded quarterfinal line-up in the top half of the draw. Diyas and Han will play each other for a place in the semifinals tomorrow, while Duan will take on No.5 seed Kateryna Kozlova, who beat wildcard Lu Jia-Jing 6-3, 6-2.

By contrast, the bottom half will be all-unseeded. Zvonareva will face Uzbekistan's Sabina Sharipova, who took out No.8 seed Jana Fett 6-4, 4-6, 6-2; and Diatchenko will battle Chinese wildcard Zhang Kai-Lin. Playing just her second tournament since Roland Garros, Zhang - whose ranking has fallen from a career high of No.103 exactly a year ago to No.264 - upended No.9 seed Arina Rodionova 6-4, 7-5.