Four-times champion Martina Hingis recovered from a poor start to beat third seed Nathalie Dechy 4-6, 7-5, 6-2 and advance to the Pan Pacific Open quarter-finals in Tokyo on Thursday.
The former world number one began her comeback last month, reaching the last eight of the Australian Open in her first Grand Slam since retiring through injury in 2002.
Hingis struggled to hold serve for the first set and a half but the Swiss dug in to force a third set and dominated her French opponent in the decider.
Four-times Tokyo champion Hingis next plays Maria Kirilenko after the Russian's 6-4, 6-4 victory over Serbian eighth seed Ana Ivanovic.
Hingis won the Pan Pacific Open in 1997, 1999, 2000 and 2002, sharing the record for singles titles with American Lindsay Davenport.
Slovakia's Daniela Hantuchova was another seeded casualty, the number six losing 7-6, 6-2 to Australia's Samantha Stosur.
Top seed and defending champion Maria Sharapova will play American Lisa Raymond later on Thursday in the $1.3 million event.