Serena Williams cruises into fourth round at Miami Open

KEY BISCAYNE, Fla. -- Eight-time champion Serena Williams avoided the upset bug at the Miami Open on Saturday, reaching the fourth round by beating Zarina Diyas 7-5, 6-3.

The South Floridian seemed unfazed by the subtropical heat, earning her 20th consecutive victory at Key Biscayne. Earlier Saturday, Rafael Nadal retired from a match for the first time in six years as temperatures approached 90 degrees and were even higher on the sunbaked stadium hardcourt.

"I live down the street, and I'm used to these conditions," Williams said. "Even though it was a little humid, I'm used to it and I love this weather.

"Rafa played like an hour-and-a-half, two hours before me, so that makes a huge difference. So I think that he was in the most intense part of the sun, whereas I was kind of at tail end of it. But I was fine."

Next up for Williams is a date with veteran Svetlana Kuznetsova, who beat Caroline Garcia in a third-set tiebreaker 4-6, 6-2, 7-6 (6).

"It's a great matchup," Williams said of Kuznetsova. "She plays well and makes a lot of the great shots. She's actually been playing well this year. She had a couple big wins and couple good tournaments.

"Yeah, I have my work cut out for me. We'll see what happens."

In other women's play, No. 8 Petra Kvitova lost to No. 30 Ekaterina Makarova 6-4, 6-4. No. 3 Agnieszka Radwanska, the 2012 champion, eliminated Madison Brengle 6-3, 6-2.

ESPN Staff Writer Matt Wilansky and The Associated Press contributed to this report.