British world number three Andy Murray cruised to a straightforward victory over Bernard Tomic at the Sony Open but the Williams sisters had contrasting fortunes in Miami on Saturday.
Top ranked Serena overcame a slow start to turn away Japan's Ayumi Morita 6-3 6-3 in third round play, but Venus was forced to withdraw from the tournament with a back injury.
Murray, meanwhile, needed only 56 minutes to defeat sluggish Australian Tomic 6-3 6-1 in his second round match.
“I don't know if he was tired or struggling with the humidity, but he was playing pretty low percentage tennis,” Murray told reporters. “With the conditions like they were today, that played into my hands.”
Murray, runner-up to world number one Novak Djokovic last year, will face Bulgaria’s Grigor Dimitrov in the third round. Dimitrov was leading 6-4 1-1 when Italy’s Simone Bolelli was forced to retire.
Serena Williams, seeking a record sixth Miami title, fell 3-0 behind in the first set against her Japanese opponent but capitalised on four of her six break points to win.
The loss left Morita 0-19 against top 10 players, while Serena reamined on course to break a tie with Steffi Graf for the most singles titles in the tournament.
Venus Williams, however, pulled out of the tournament with a lower back injury before her match with fellow American Sloane Stephens.
Spanish wildcard Garbine Muguruza Blanco delivered the day’s biggest stunner, eliminating ninth seed Caroline Wozniacki of Denmark 6-2 6-4 in 81 minutes. Fifth seed Li Na of China, playing her first tournament since injuring her ankle in the Australian Open final, dismissed American Varvara Lepchenko 6-2 6-4.
Polish defending champion Agnieszka Radwanska collected a 7-6 2-6 6-3 win over Slovakia's Magdalena Rybarikova to advance to the fourth round.
In other men's second round play, Frenchmen Jo-Wilfried Tsonga and Richard Gasquet both won.
Rohan Bopanna and Sania Mirza advanced to the second rounds of their respective events.
Bopanna and his American partner Rajeev Ram saved all the seven breakpoints in the second set to beat Eric Butorac and Paul Hanley 7-6 (8) 6-4. They next face Marin Cilic and Lukas Dlouhy.
In the women's event, seventh seeds Sania Mirza and her American partner Bethanie Mattek-Sands defeated Eva Birnerova and Varvara Lepchenko 7-5 6-3 in one bour and 21 minutes.