Li Na had to overcome illness and a dogged Anastasia Pavlyuchenkova to reach last 16 of the Pan Pacific Open.
The former French Open champion has been struggling with a nasty cough but her experience was crucial as the seventh seed managed to win 7-5 4-6 6-2 in two hours, 37 minutes.
However 2011 Wimbledon champion Petra Kvitova suffered an upset as she crashed out in straight sets to Petra Martic.
The fourth seed had her chances but she could not live with Martic's serve as she slipped to a 6-4 6-4 loss.
Martic's reward is a last 16 tie with Nadia Petrova after the 17th-seeded Russian saw off Simona Halep 7-6 6-0.
Angelique Kerber made short work of wildcard Ayumi Morita as the fifth seed raced to a 6-3 6-4 victory, while No.6 seed Sara Errani overcame Johanna Larsson 6-3 7-6.
Ninth seed Marion Bartoli is also through after her 6-2 7-5 win over Julia Goerges.
