Newly crowned world number one Garbine Muguruza pulverised Olympic champion Monica Puig 6-4, 6-0 on Wednesday to reach the quarter-finals of the Pan Pacific Open.
Earlier, second seed Karolina Pliskova, who held the top ranking briefly over the summer, crushed Poland's Magda Linette 6-2, 6-1 as the Czech set up a clash with another former world number one, Angelique Kerber.
Wimbledon champion Muguruza recovered from an indifferent start to reach the last eight in Tokyo, the top seed catching fire after a trade of early breaks to rattle off the last seven games.
A booming serve down the middle sealed the first set for the Spaniard, who seemed intent on hitting the fur off the ball in her first match since reaching the top of women's WTA rankings last week.
Muguruza, chasing a third title of the year, roared through the second, a murderous backhand pass giving her a 3-0 lead to effectively kill off any hopes Puig had of mounting a comeback.
The Puerto Rican, who upset Muguruza on her way to winning a shock gold medal at last year's Rio Olympics, fell apart thereafter as her Spanish tormentor turned the screw, bringing the match to a close with an ace after an hour and 14 minutes.
"The last time I played her it didn't go my way at all," Muguruza told reporters.
"I'm also happy to win my first match as number one. To be honest nothing has really changed but I know every match is going to be even tougher now."
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Pliskova likewise tore through her second-round match, the world number four taking exactly an hour to see off Linette.
A ferocious forehand gave the Czech an early break in the first set, which she pocketed thanks to a clinical cross-court backhand.
The second set was almost a carbon copy as Pliskova again raced to a 3-0 lead before a thunderous backhand pass brought a double break.
The end came mercifully swiftly for a dejected Linette, who wafted a Pliskova serve wide on match point to sum up her contribution to a lop-sided contest.
"The number one ranking is not really my goal," insisted Pliskova, chasing a fourth title of the year and 10th of her career.
"It would be great to end the year there," added the 25-year-old, who beat Linette in the first round of the US Open by the same score before losing in the quarter-finals earlier this month.
"But my aim right now is just to try to win more titles."
German Kerber booked her place in the quarter-finals with a 7-6, 6-3 victory over Russia's Daria Kasatkina in the day's late match.
Elsewhere, China's Wang Qiang failed to capitalise on her stunning 6-0, 6-0 ambush of eighth seed Kristina Mladenovic as she was bundled out 6-4, 4-6, 6-2 by Russian Anastasia Pavlyuchenkova.
Muguruza heads a strong field in Tokyo featuring several top 10 players including Pliskova, Johanna Konta and defending champion Caroline Wozniacki.