Two-time champion Maria Sharapova overpowered Lucie Safarova of the Czech Republic 6-2, 7-6 (5) to advance to the Pan Pacific Open quarterfinals on Wednesday.
The second-seeded Sharapova was coming off a tough, three-hour win over British qualifier Heather Watson on Tuesday, while Safarova advanced to the third round on a walkover.
Sharapova coasted through the first set and led 3-0 before Safarova mounted a comeback, breaking Sharapova three times to take a 6-5 lead.
"After a long match yesterday I was really happy to win in two sets"
Sharapova broke Safarova in the final game to force a tiebreaker which she won with an ace after 1 hour, 43 minutes. However, the Russian struggled with her serve and double-faults on big points almost cost her the second set as the sun set over Tokyo.
"After a long match yesterday I was really happy to win in two sets,'' Sharapova said.
"I had a bit of a letdown in the second set but was really happy that I could close it out in the tiebreaker.''
Sharapova will face Sam Stosur in the quarterfinals. The eighth-seeded Australian beat Dominika Cibulkova of Slovakia 6-4, 7-5.
In other matches, Sara Errani of Italy beat Marion Bartoli 3-6, 6-2, 6-2 while Nadia Petrova of Russia beat Petra Martic of Croatia 7-6 (2), 6-7 (1), 6-4.
After struggling in the first set, the sixth-seeded Errani broke Bartoli in the second game of the second set and never looked back.
"It was a tough match on this fast court,'' said Errani, who has won three titles this year.
"I didn't start off well but neither did she. She got a little tired in the second set and that's when I started to play better.''
Top-ranked Victoria Azarenka faced Roberta Vinci of Italy later on Wednesday.