Swiss top seed Belinda Bencic and Belarusian defending champion Aryna Sabalenka were both knocked out on a day of upsets at China's Shenzhen Open on Tuesday.
Russia's Anna Blinkova claimed the first top-10 win of her career when she came from behind to beat Bencic 3-6 6-3 6-3 in the first round while Sabalenka was beaten 6-4 6-4 by the Czech Republic's Kristyna Pliskova in the last-16.
21-year-old Blinkova started poorly against world number eight Bencic and was broken three times in the opening set. But she never dropped her serve thereafter, firing 12 aces and breaking Bencic five times to advance to the second round in a little under two hours.
"It was a great performance from me today," world No.58 Blinkova said.
"I prepared very carefully and I'm happy that I played good tennis. I was thinking to just fight for every point.
"I didn't feel great in the beginning of the match, I didn't feel the ball and my shots. I didn't play bad, but I managed to increase the level of my game slowly, step by step."
Second seed Sabalenka had 11 break points in the match, including nine in the second set, but could not convert even one as a dogged Pliskova served well under intense pressure.
"My serve was there, which is always important, so I'm happy that I won," Pliskova said.
"I reached the quarter-finals here two years ago, so I'm happy to be back there and looking to see if I can do more."
It was not a good day for the Chinese with Wang Xiyu falling 6-4 6-3 to third seed Elise Mertens of Belgium.
Eighth seed Zhang Shuai was beaten 7-6 (12-10) 6-3 by Ukraine's Kateryna Bondarenko, while Wang Yafan went down 6-3 6-4 to seventh seed Elena Rybakina of Kazakhstan.