Garbine Muguruza breezed into quarter-finals of the Pan Pacific Open with a straight-sets victory over Monica Puig in her first match as world number one.
The Wimbledon champion replaced Karolina Pliskova at the top of the rankings last week and showed no signs of being burdened by her new status in a 6-4 6-0 win over Puig.
Top seed Muguruza, back in action for the first time since losing to Petra Kvitova in the fourth round of the US Open, was broken only once in the match and will take on Caroline Garcia or Kurumi Nara in the last eight.
Muguruza won the first two games of the second-round contest in Tokyo on Wednesday and regained the initiative after Puig had hit back to level at 2-2, a second break enough for the Spaniard to take the first set.
Olympic champion Puig was blown away in the second set, Muguruza winning 12 points in a row to race into a 4-0 lead as she eased through with a dominant display.
Former world number ones Pliskova and Angelique Kerber will meet in the quarter-finals after advancing at the expense of Magda Linette and Daria Kasatkina respectively.
Pliskova defeated the unseeded Pole 6-2 6-1, the second seed's power proving to be too potent in a match that lasted just an hour.
Kerber stopped the rot following first-round exits at Flushing Meadows and in Cincinnati, seeing off Kasatkina 7-6 (7-5) 6-3 after losing the first three games in an alarming start.
Anastasia Pavlyuchenkova earlier got the better of Wang Qiang 6-4 4-6 6-2.