Top-seeded Caroline Wozniacki beat Ana Konjuh 6-2, 6-2 to advance to the quarter-finals of the Pan Pacific Open.
Wozniacki had a first-round bye and faced little resistance from the Croatian qualifier in a match that lasted just over 80 minutes at Ariake Colosseum.
The Dane won five of nine break points to set up a quarterfinal with fifth-seeded Angelique Kerber of Germany who rallied to defeat Madison Brengle of the United States, 5-7, 6-1, 6-0.
"It's always tough when you haven't played matches for a while so I'm just happy to win this one and be through to the next round," said Wozniacki, whose last outing was a second-round loss to Petra Cetkovska at the US Open.
"There are a few things I want to work on but I'm happy with the victory."
Wozniacki, who won here in 2010, improved to 2-0 against Konjuh.
Third-seeded Garbine Muguruza of Spain beat Barbora Strycova of the Czech Republic 6-3, 6-4 and next faces eighth-seeded Belinda Bencic of Switzerland.
Bencic rallied to beat Samantha Stosur 6-7 (5), 6-3, 6-4.
It was Bencic's first win against the Australian veteran who lost despite hitting 13 aces.
Muguruza and Bencic will be playing against each other for the first time.
1-Caroline Wozniacki (Denmark) beat Ana Konjuh (Croatia) 6-2 6-2
5-Angelique Kerber (Germany) beat Madison Brengle (U.S.) 5-7 6-1 6-0
8-Belinda Bencic (Switzerland) beat Samantha Stosur (Australia) 6-7(5) 6-3 6-4
3-Garbine Muguruza Blanco (Spain) beat Barbora Strycova (Czech Republic) 6-3 6-4