Venus all smiles after straight sets win

Williams, who will next play Angelique Kerber after the top seed cruised by Japanese qualifier Risa Ozaki 6-2 6-2, is a three-time champion in Miami and first played in the tournament as a 16-year-old.

“I was still in braces, it’s been a long time,” she said in a post-match interview.

The 36-year-old delivered exquisite shot-making during a rally on match point to eliminate the twice major champion Kuznetsova.

Her next opponent Kerber was barely tested in her 62-minute match, feasting off her opponents' serve, while second seed Karolina Pliskova also reached the quarter-finals as she beat 15th-seeded Czech compatriot Barbora Strycova 6-1 6-4.

Pliskova cruised through the 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. Pliskova recovered to take the final game.

French Open champion Garbine Muguruza retired from her match with Caroline Wozniacki after dropping the first set. The sixth seed took a medical timeout after dropping the first set 7-6(1) to Wozniacki and decided she was unable to continue.

“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.”

Wozniacki has now advanced to her sixth quarter-final in seven 2017 events.

In other women's matches, third seed Simona Halep overcame Australian Samantha Stosur 4-6 7-5 6-2, and 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.