Number one seed Caroline Wozniacki outclassed Ana Konjuh of Croatia 6-2, 6-2 at the Pan Pacific Open Wednesday, advancing to a quarter-final against German fifth seed Angelique Kerber.
The Danish former world number one, winner here in 2010, took one hour and 22 minutes to complete the night match.
"Overall, I am happy with the victory," said Wozniacki, who is currently the world number six.
Kerber has won six of her past 10 meetings with Wozniacki, including the April final of the Porsche Tennis Grand Prix in Stuttgart, Germany.
Swiss teenager Belinda Bencic edged past former US Open champion Samantha Stosur in a gruelling second-round thriller.
The 18-year-old, ranked 15th in the world, spent two hours and 16 minutes to win 6-7 (7/5), 6-3, 6-4, surviving constant pressure from the big serves and sizzling returns of the 22nd-ranked Australian.
The victory means Bencic will play her first match against Spanish third seed Garbine Muguruza in the quarter-finals.
"It was very tough for me to return," Bencic said. "I am realy happy that I was able to win such a difficult match."
Early on in the match, Bencic beame visibly frustrated with her mistakes, suffering three double faults in the first set while Stosur demonstrated her finesse with seven aces.
But Stosur decelerated in the second set as Bencic found her rhythm to end the set 6-3.
The Australian veteran came back late in the third set, when she narrowed a 4-0 deficit to 4-3, causing her teenage opponent to have a chat with her coach who is also her father.
The young star in the end managed to maintain her momentum to grab victory.
"I tried to be relaxed, but of course it was a tight game. I just wanted to talk with my dad what to do in next two games so I can win the match," Bencic said.
"It was a difficult situation mentally. It`s good that I stayed calm in that."
In other matches Muguruza, the world number eight, outperformed Czech Barbora Strycova 6-3, 6-4.
Kerber came behind for a 5-7, 6-1, 6-0 victory against American Madison Brengle.