International Sports Desk, Mar 24 (EFE).- American Venus Williams, the 19th seed, pulled out of the Sony Open in Miami before her match against countrywoman Sloane Stephens due to back problems.
The 32-year-old Williams, who won the title in Miami in 1998, 1999 and 2001, is a former world No. 1 who has won seven Grand Slam titles.
The 20-year-old Stephens will play defending champion Agnieszka Radwanska of Poland next.
Radwanska struggled in her 7-6 (7-5), 2-6, 6-3 victory over Slovakia's Magdalena Rybarikova at the Crandon Park tennis center on Key Biscayne.
In other action at the Sony Open on Saturday, Spain's Garbiñe Muguruza defeated Denmark's Caroline Wozniacki, the 9th seed, 6-2, 6-4 in a second-round meeting.
Muguruza, who is ranked No. 73 in the world, needed just 81 minutes to beat the former world No. 1, who appeared unable to figure out the Spanish player's game.
Muguruza's next opponent will be China's Li Na, the No. 5 seed, who beat American Varvara Lepchenko 6-2, 6-4.
On the men's side, Colombia's Alejandro Falla beat Spain's Fernando Verdasco 6-3, 7-6 (8-6) in one hour and 44 minutes.
Falla will take on the Czech Republic's Tomas Berdych, the No. 4 seed, next.
Berdych defeated Spain's Daniel Gimeno 5-7, 7-6 (7-3), 6-2.