Defending Agnieszka Radwanska passed a stern test from Barbora Strycova to reach the quarter-finals of the Pan Pacific Open, but Petra Kvitova suffered another defeat to Monica Puig on Wednesday.
Playing her first match since suffering a shock fourth-round defeat to Ana Konjuh at the US Open, second seed Radwanska fought back time and time again in the final set to win 6-3 3-6 7-5 in Tokyo.
The world number four was a break down on three occasions in the decider, but hung in there to set up an encounter with Olympic champion Puig.
Radwanska, still to secure her place in the season-ending WTA Finals tournament which she won last year, was broken seven times by the unseeded Strycova before finally ending the Czech's bold challenge in a contest which swung this way and then other.
Kvitova, winner of the tournament in 2013, was beaten by Puig in the semi-finals of the Rio Olympics last month and the Puerto Rican pulled off a gutsy fightback to beat the two-time Wimbledon champion again at the Ariake Tennis Forest Park.
The seventh seed led 4-2 in the final set, but Puig reeled off four games in a row to seal a 1-6 6-4 6-4 triumph and book her place in the last eight after saving 10 break points in another battling display.
Wildcard Naomi Osaka also pulled off an upset, getting the better of sixth seed Dominika Cibulkova 6-2 6-1 in just 63 minutes, while US Open semi-finalist Caroline Wozniacki dumped out fourth seed Carla Suarez Navarro with a 7-6 (7-4) 4-6 6-4 victory.