(Reuters) - Top seeds Angelique Kerber and Karolina Pliskova reached the Miami Open quarter-finals while French Open champion Garbine Muguruza retired from her match with Caroline Wozniacki after dropping the first set.
German Kerber, the top seed, cruised by Japanese qualifier Risa Ozaki 6-2 6-2 while Czech second seed Pliskova beat 15th-seeded compatriot Barbora Strycova 6-1 6-4.
Kerber was barely tested in her 62-minute match during which she displayed a great arsenal of shots and was all over her opponents' serve.
She moves on to face the winner of Monday's round of 16 clash between Venus Williams and Russian seventh seed Svetlana Kuznetsova.
Pliskova cruised through her first set in 22 minutes and looked ready to wrap up a quick victory when she went ahead 5-2 in the second but Strycova found life late in the match breaking Pliskova then holding at love.
"Everything was fine, going well, until 6-1, 5-2," Pliskova, who fought off three break points in the final game, said in a report on the WTA website.
"I was happy to close it because the end was tricky - the end was a little bit shaky."
Sixth seed Muguruza took a medical timeout after dropping the first set 7-6(1) to Wozniacki after feeling dizzy and decided she was unable to continue against the Dane.
"I started normal, and then like at 3-3 or something like this I started to feel headache, pain in my stomach," Muguruza said. "And then it kind of went more and more during the match.
"When I was getting to the 5-4, something like this, I started to feel a little bit dizzy. I think it was the heat? The heat affected me suddenly like that."
With the win, Wozniacki advanced to sixth quarter-final in seven 2017 events.
In other women's action, former Czech world number five Lucie Safarova beat Slovakian fourth seed Dominika Cibulkova 7-6(5) 6-1 to reach the last eight.
For unseeded Safarova, who is on the comeback trail from a bacterial infection that hampered her for parts of the past two seasons, the win marked her first top-10 victory since 2015.
(Reporting by Frank Pingue in Toronto. Editing by Steve Keating.)