World number three Garbine Muguruza crashed out of the Wuhan Open in the second round at the hands of Jelena Jankovic on Tuesday.
The second seed received a bye into round two but was eliminated in straight sets by the former world number one, who claimed a 6-4 7-6 (7-2) victory.
There was no such disappointment for Angelique Kerber, who won her first match since overtaking Serena Williams as world number one, coming from a set down to beat Kristina Mladenovic 6-7 (4-7) 6-1 6-4.
She will now face Petra Kvitova after the two-time Wimbledon champion dispatched Elina Svitolina 6-3 6-1, while sixth seed Venus Williams overcame Yulia Putintseva 6-3 6-2 to set up a last-eight clash with Svetlana Kuznetsova - a 6-0 6-4 winner over Madison Brengle.
Third seed Agnieszka Radwanska is through after easily knocking out Ekaterina Makarova, but faces a tricky quarter-final against a resurgent Caroline Wozniacki.
MORE MISERY FOR MUGURUZA
French Open champion Muguruza's poor form continued against Jankovic as she followed up her second-round defeat at the US Open and quarter-final loss at the Pan Pacific Open with another early exit.
It was an error-strewn display from the Spaniard, Muguruza committing 42 unforced errors, with Jankovic taking full advantage in building on her to run the final at the Guangzhou International Open.
"I felt like I was in control of the match, but the last shot was not there," Muguruza said afterwards. "I made maybe too many mistakes against Jankovic, the type of girl which is very solid."
Jankovic will take on Barbora Strycova in the quarters following the Czech's 5-7 6-0 6-2 success against Misaki Doi.
KERBER SURVIVES SCARE
It took the new world number one some time to find her rhythm against world number 54 Mladenovic.
The Frenchwoman recovered from spurning set points in the first set to take the opener in a tie-break, but it was one-way traffic in the second as Kerber forced a decider in emphatic fashion after a pep talk from coach Torben Beltz at the changeover.
Mladenovic refused to lie down despite being broken to love in the first game of the third but she was unable to make an impact on Kerber's serve, the German's quality and consistency winning through.
Of her upcoming match wiith Kvitova, who she beat en route to the US Open title, Kerber said: "It's always a tough battle against Petra. I will have to play my one of my best tennis tomorrow against her."
WOZNIACKI SETS UP RADWANSKA REUNION
Wozniacki has seen off some impressive names in her startling late-season revival, which has seen her reach the semi-finals of the US Open and win the Pan Pacific Open.
Radwanska was one of the players to fall victim to Wozniacki in Tokyo, losing in three sets in the last four, and will have a chance for revenge after a 6-4 6-1 defeat of Makarova.
Dane Wozniacki had a tougher time against qualifier Katerina Siniakova, winning 6-4 6-4 in a contest featuring a second set that started with seven straight breaks of serve.
VENUS CONTINUES TITLE DEFENCE
A retirement by Muguruza in last year's final handed Williams the title last year and the seven-time grand slam champion needed only an hour and 10 minutes to progress to the quarters, breaking Putintseva seven times en route to victory.
Compatriot Madison Keys came through 6-3 6-4 against Caroline Garcia, Dominika Cibulkova recovered from a set down to beat Laura Siegemund 2-6 6-3 6-4 and Johanna Konta saw off Zhang Shuai 6-3 6-3.
Roberta Vinci's tournament is over after the 13th seed lost to Yaroslava Shvedova 7-5 6-2 and Daria Kasatkina defeated fellow qualifier Louisa Chirico 6-1 6-1 in just under 50 minutes.