Garbine Muguruza cruised to victory in her first match as world No. 1, comfortably beating Rio Olympic champion Monica Puig in straight sets at the Toray Pan Pacific Open on Wednesday.

Wimbledon champion Muguruza, who unseated Karolina Pliskova at the top of the WTA rankings on Sept. 11, advanced to the quarterfinals with a 6-4, 6-0 win against Puig at Ariake Colosseum.

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Puig had won their only previous meeting in the round of 16 at Rio last year, when the Puerto Rican stormed to the gold medal. But on Wednesday, it was all Muguruza, who played like the world's top-ranked player, while Puig committed far too many unforced errors to stand a chance.

Muguruza, only the second woman from Spain to climb to No. 1 after Arantxa Sanchez Vicario, was pleased to start this phase of her career on the right foot.

"I'm actually very happy because it was my first match as No. 1," Muguruza said. "And I'm happy because the last time I played her it didn't go my way at all and this time, I found a better way to play and got the victory."

"I think on paper it's different. But I'm not thinking, 'Oh I'm No. 1, I should win easily' or anything like that. I have to be ready and every match is going to be tougher now."

In her quarterfinal, Muguruza will face either France's Caroline Garcia or Kurumi Nara, the last remaining Japanese in the field.

"It's always good to be in Tokyo, playing my first tournament in Asia (this season)," Muguruza said. "I kind of always have good results so I'm happy it's going well this year as well."

The two kept it close in the first set, splitting the first four games before Muguruza captured what turned out to be the crucial fifth, a love game aided by one of Puig's five double faults in the match. Muguruza went on to take a 4-2 lead and from that point on, traded game for game to eventually win the set.

Puig started the second set horribly, double faulting twice to hand Muguruza one of her five break points. Riddled by mistakes, the match rolled downhill fast for Puig, with her opponent acing match point to reach the next round.

Muguruza insisted the contest was a lot closer than it seemed.

"She played very well in the Olympic Games. That day I didn't play well but all credit to her," she said. "I think I improved a lot as well. I've had a good year, I'm a little bit more confident and I knew how to go out there and be aggressive."

"In the second set, I kind of learned what I did well in the first set. She also made a few more mistakes and I made a few more good shots. I think it was just a few things different."

The woman who Muguruza displaced in the rankings, Karolina Pliskova, outclassed Polish qualifier Magda Linette in straight sets.

Pliskova, the second seed behind Muguruza, brushed aside Linette 6-2, 6-1 in 60 minutes to reach the quarterfinals, where she will face either former U.S. Open champion Angelique Kerber or Daria Kasatkina of Russia.

"I felt great today on the court," Pliskova said. "My serve was working well and I felt I had pretty good depth on my shots so I'm really happy with the win today."

"I think it was a good start."

Fourth-ranked Pliskova had owned her matchups against Linette 5-1 over their careers going into Wednesday, and the Czech continued to lord it over the No. 76 at Ariake Colosseum.

Pliskova held serve throughout the match while converting four of 10 break-point opportunities. Behind her serve which topped 180 kilometers per hour, Pliskova aced Linette eight times and won a whopping 91 percent of points off her first service.

Linette just never looked capable of matching Pliskova with a majority of the few points she managed to win coming on unforced errors.

The two most recently clashed in the first round of the U.S. Open, where Pliskova also prevailed in two sets. Pliskova said that experience proved useful.

"We played in New York against each other so I know a little bit what to expect from her," she said. "She also didn't play the best today and I was feeling well. Like I said, my game was working today."

Russia's Anastasia Pavlyuchenkova defeated Wang Qiang of China 6-4, 4-6, 6-2 and will meet either fourth seed Johanna Konta or Barbora Strycova in the last eight.