Top-seeded Agnieszka Radwanska of Poland eased into the quarter-finals of the Eastbourne International with a 6-3 6-3 win over Eugenie Bouchard of Canada on Wednesday.
But former champion Caroline Wozniacki was upset by Puerto Rican qualifier Monica Puig, who won their third-round match 4-6 6-3 6-4.
Fifth-seeded Czech and two-time Wimbledon winner Petra Kvitova was also beaten as Britain's Johanna Konta recovered from the disappointment of dropping the opening set after leading 5-2.
Konta avenged her defeat to Kvitova at the 2015 US Open by winning 5-7 6-4 6-0 to leave the Czech still searching for her first title since August.
Wozniacki, who won the title in 2009, is struggling to regain form after missing the entire clay-court season with a right ankle injury. The Dane has managed just three wins in three tournaments since her return.
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"You don't climb Mount Everest in one day," said Wozniacki.
"I played really well. I'm really happy with that ... the foot, the body's feeling good."
Although Wozniacki fought off four break points that would have given Puig a 4-2 lead in the opening set, she was unable to seriously pressure a confident opponent who recently reached the Nottingham semifinals.
"She's a great player and she makes you work for every single point," said Puig.
Russian 2013 champion Elena Vesnina kept on track with a 7-6 (7-2) 6-4 win over American qualifier Madison Brengle.
TDominika Cibulkova also reached the quarterfinals of the grass-court tournament by overcoming Ukrainian qualifier Kateryna Bondarenko 7-6 (3), 6-3, and there was victory too for Kristina Mladenovic of France, who beat Germany's Anna-Lena Friedsam 6-4 7-6 (7-4).
The two remaining third-round matches were suspended overnight due to rain.
