MIAMI, FL, USA - Three players who have combined for nine Sony Open Tennis titles headline the action as third round play gets underway.
Saturday, Third Round
 Sloane Stephens (USA #16) vs.  Venus Williams (USA #18)
Head-to-head: first meeting
Though three-time Miami champion Venus Williams has never played Sloane Stephens, sister Serena knows all about what she is capable of. Stephens stunned Serena Williams in the quarterfinals of January's Australian Open en route to the semifinals, showing she is no longer a future star but a current one. After that, Stephens cracked the Top 20 and became the second-highest ranked American. In her opener here on Thursday, the day after she turned 20, Stephens recovered from a nightmare 6-0 first set loss to defeat Olga Govortsova.
Williams was also tested in her opener, needing seven match points to overcome Kimiko Date-Krumm and improve to 52-10 here. She returned from a seven-month break because of illness a year ago in Miami at No.134 and a strong 12 months since, including a title in Luxembourg last October, has her back inside the Top 20.
 Serena Williams (USA #1) vs. Ayumi Morita (JPN #50)
Head-to-head: Williams leads 1-0
Playing her first tournament since returning to World No.1 is Serena Williams. Tied with Steffi Graf for the most titles in Miami history with five, Williams cruised past Flavia Pennetta in her opener to improve her event record to 56-7. In addition to trying to pass Graf, Williams also will be motivated to keep Maria Sharapova from taking her top spot. She needs to get to at least the quarterfinals, with Sharapova not winning the title, to assure herself of staying No.1. She has never lost before the fourth round here.
Though Ayumi Morita is 0-18 against Top 10 players, she did record her career-best win over No.13 Ana Ivanovic in Pattaya City last month. Since then she added her fifth Top 20 win and tied for her best WTA outing with a semifinal showing in Kuala Lumpur.
 Agnieszka Radwanska (POL #4) vs. Magdalena Rybarikova (SVK #49)
Head-to-head: Radwanska leads 3-1
A terrific 2012 campaign saw Agnieszka Radwanska capture three titles, including her biggest to date in Miami. Already with two titles in 2013, Radwanska picked up her 20th win of the year with a straight set defeat of Hsieh Su-Wei in her Miami opener. Only Sara Errani has more wins so far this season.
Magdalena Rybarikova will be looking for her 10th Top 20 win but her first versus a Top 5 opponent. The second of her two straight set victories so far this week was an impressive upset of World No.23 Mona Barthel. Her 2013 season has been highlighted by a semifinal showing in Memphis and quarterfinal appearance in Florianopolis.