Tokyo - New world number one Garbine Muguruza overpowered France's Caroline Garcia 6-2, 6-4 on Friday to reach the semi-finals of the Pan Pacific Open.
Earlier former number one Angelique Kerber won a war of attrition with second seed Karolina Pliskova to book her place in the last four.
Spaniard Muguruza, playing her first tournament since reaching the top of the women's world rankings, never looked threatened in a one-sided quarter-final.
The Wimbledon champion stormed to a 5-1 lead before ripping a half-court forehand into the corner to secure the first set.
Muguruza pounced on a short second serve with a murderous backhand to break early in the second and the top seed dealt calmly with fleeting resistance from Garcia.
The ninth seed gave herself a lifeline to level the set at 3-3 but was quickly put in her place when Muguruza beat her with a ferocious backhand pass to restore normal service.
A crunching serve down the middle put Garcia out of her misery after 81 minutes as Muguruza advanced to face either title-holder Caroline Wozniacki or Slovakia's Dominika Cibulkova.
Kerber, seeded seventh and a former Tokyo finalist, came through 7-6 (7/5), 7-5 as she repelled some brutal hitting from her Czech opponent in a contest of real quality.
Pliskova, who herself briefly held the women's top ranking over the summer, produced moments of brilliance at the net but ultimately crumbled under relentless pressure from the German.
One of her eight double-faults gifted Kerber the first-set tiebreak 7-5 before Pliskova unravelled again at the business end of the second set.
Kerber turned the screw in the 12th game, forcing Pliskova to save four match points before delivering the coup de grace with a vicious, dipping backhand that landed on the Czech's shoelaces, giving her no chance.
The 29-year-old Kerber, who has slipped back to 14th in the world since winning last year's Australian and US Open titles, faces Anastasia Pavlyuchenkova in the last four.
The Russian advanced by overcoming another Czech, Barbora Strycova, 5-7, 6-3, 6-1.
"Right now there's no pressure on me at all," said Kerber, the 2013 runner-up.
"I've had a few ups and downs this year but I know I can still beat the best players in the world. I showed today I can play like I did last year."
Results of singles matches at the Pan Pacific Open women's tennis tournament in Tokyo on Friday (x denotes seeding):
Garbine Muguruza (ESP x1) bt Caroline Garcia (FRA x9) 6-2, 6-4
Angelique Kerber (GER x7) bt Karolina Pliskova (CZE x2) 7-6 (7/5), 7-5
Anastasia Pavlyuchenkova (RUS) bt Barbora Strycova (CZE) 5-7, 6-3, 6-1