Carla Suarez Navarro was the sole seed to fall in Thursday's second-round action at the Pan Pacific Open.
The Spaniard's form has totally deserted her in recent months, with first-round defeats at Wimbledon and the US Open falling into a run of seven straight defeats, which was snapped by Tuesday's victory over Kateryna Bondarenko in Tokyo.
However, that proved a false dawn for the world number 10 – three times a finalist on Tour this year before her slump.
Dominika Cibulkova did the damage with a 6-4 6-4 success – improving her head-to-head record against Suarez Navarro to 2-0.
Cibulkova's quarter-final opponent is second seed Ana Ivanovic, who saw off the dangerous Camila Giorgi 7-5 6-2.
Giorgi came into the game with an impressive 6-6 record against top-10 opposition, but was little match for the former world number one.
"It was a very tough match tonight," Ivanovic said. "She's playing well, and she generates so much power off her groundstrokes and serve.
"I really had to stay low because she has such a powerful game. I knew I had to stay composed in the first set, and then stay on top of her in the second set, because if you let her play her game, she can play really well. I knew she would be dangerous so I'm happy I made it."
Agnieszka Radwanska kept up her record of reaching the quarter-finals in every appearance at this tournament, doing so for a seventh time with a 6-4 6-1 win over Elina Svitolina, where Karolina Pliskova awaits after a 6-2 6-4 win over Japanese number one Kurumi Nara.