KEY BISCAYNE, Fla. -- Venus Williams defeated seventh-seeded Svetlana Kuznetsova 6-3, 7-6 (4) in a matchup of former Miami Open champions on Monday to reach the quarterfinals.
Williams fended off two set points to get into the tiebreaker, and then rallied from 4-1 down in the decider to win the match in two sets.
Williams will meet next top-seeded Angelique Kerber, who made it to the quarterfinals after beating Risa Ozaki 6-2, 6-2.
Caroline Wozniacki also advanced on Monday to the next round after Garbine Muguruza retired with a heat-related illness.
Wozniacki, the 12th seed, took the first set 7-6 over the sixth-seeded Muguruza. The Spaniard was tended to by doctors after the tiebreaker and decided she could not continue on a 77-degree, humid afternoon in South Florida. She said she began feeling a headache and stomach pain midway through the set, then experienced some dizziness.
"Kind of went more and more during the match," Muguruza said.
Wozniacki still has not dropped a set in the tournament and will next face Lucie Safarova in the quarterfinals. Safarova upset fourth-seeded Dominika Cibulkova 7-6, 6-1.
Earlier Monday, Karolina Pliskova also reached the quarterfinals, beating Czech Fed Cup teammate -- and occasional doubles partner -- Barbora Strycova 6-1, 6-4. Pliskova needed only 21 minutes to take the first set, winning 11 consecutive points in one stretch and 16 of 17 on her serve.
"I was expecting a tough battle," Pliskova said. "It was tricky in the end, but I'm glad I won."
Third-seeded Simona Halep dropped the first set before beating 14th-seeded Samantha Stosur. Other women's quarterfinal spots went to 10th-seeded Johanna Konta and 26th-seeded Mirjana Lucic-Baroni.