Tokyo — Former champion Caroline Wozniacki outlasted fourth-seeded Carla Suarez Navarro 7-6 (4), 4-6, 6-4 to advance to the Pan Pacific Open quarter-finals on Wednesday.
Wozniacki won four of five break points in the nearly three-hour match at Ariake Colloseum.
"We played for such a long time and ... the standard was very high," Wozniacki said.
"Luckily, I'm the one here, and I'm happy to get through."
Wozniacki, who won the title in 2010 and reached the final in 2014, looked set for a comfortable win but Suarez Navarro reeled off four straight games to take the second set.
A sudden rain delay at the start of the third set took the momentum away from Suarez Navarro as the Spaniard double-faulted to slip a break behind.
Wozniacki served out, and will meet either Yulia Putintseva or Magda Linette in the quarterfinals.
Second-seeded Agnieszka Radwanska also faced a major challenge but prevailed over Barbora Strycova of the Czech Republic 6-3, 3-6, 7-5.
Radwanska will next face Monica Puig, who rallied to upset 2013 champion Petra Kvitova 1-6, 6-4, 6-4.
The Puerto Rican, who also beat Kvitova on her way to becoming the Rio de Janeiro Olympic champion, recovered from 4-2 down in the final set. She saved 10 of 13 break points.
Japanese wild card Naomi Osaka beat sixth-seeded Dominika Cibulkova of Slovakia 6-2, 6-1 to set up a quarterfinal with either Karolina Pliskova or Aliaksandra Sasnovich.