Garbine Muguruza of Spain in action against Petra Kvitova of the Czech Republic during their fourth round match at US Open in New York, US, Sept 3, 2017. [Photo/Agencies]

TOKYO - New world number one Garbine Muguruza overwhelmed Olympic champion Monica Puig 6-4 6-0 to ease into the quarter-finals of the Pan Pacific Open in Tokyo on Wednesday.

Playing her first match since taking over at the top, Spain's Wimbledon champion broke her Puerto Rican opponent twice in the first set and was even more dominant in the second.

Puig dropped serve in the first game of the match but used her impressive court coverage to restore parity in the fourth game before Muguruza seized control of the contest when she broke her opponent again in the next game.

After winning the first set, the 23-year-old Muguruza moved up a gear to race away from her 70th ranked opponent and sealed victory with her third ace after 75 minutes.

"It's a big change for me," top seed Muguruza said in a courtside interview when reminded she had entered the tournament five years ago as a qualifier.

"I improved so much and I think everybody can see it. I'm very happy about that," added the Spaniard, who will meet either home wildcard Kurumi Nara or Caroline Garcia of France in her fourth successive quarter-final appearance in the event.