MIAMI, FL, USA - All eight quarterfinal berths in the singles competition at the Sony Open Tennis will be decided on Monday, with Li Na, Agnieszka Radwanska and Sara Errani among those looking to progress.
Monday, Fourth Round
 Li Na (CHN #5) vs. [WC] Garbiñe Muguruza (ESP #73)
Head-to-head: Li leads 1-0
After a slow start to the year, Garbiñe Muguruza has really found her feet over the past few weeks on the hardcourts on either side of the United States. Following on from an encouraging run through qualifying and into the fourth round at Indian Wells, the Spanish teenager has now reached the same stage in Miami.
And she has looked impressive in doing so, defeating Anastasia Pavlyuchenkova and Caroline Wozniacki in the past two rounds. The second of these victories was her second over a Top 10 player and she will need to find a similar level if she is to stand a chance of making it three. Li Na, her last 16 opponent, may be playing her first tournament since her Australian Open final defeat but has looked anything but rusty, swatting aside first Kiki Bertens and then Varvara Lepchenko in straight sets.
 Agnieszka Radwanska (POL #4) vs.  Sloane Stephens (USA #16)
Head-to-head: Radwanska leads 1-0
Twelve months ago, Sloane Stephens, then barely inside the Top 100, had to negotiate two rounds of qualifying just to make the main draw in Miami. This time around, the 20-year-old, who grew up 30 miles up the coast in Plantation, is among the Top 16 seeds and an outside bet for the title.
However, despite her elevated status, things have not gone entirely to plan of late, with Stephens winning just two matches since January's semifinal run at the Australian Open. Defending champion Agnieszka Radwanska, on the other hand, has been the picture of consistency this year, consolidating her Top 5 status with two titles and a 21-4 record. The Pole won the only previous meeting between the two, in Cincinnati last summer, and, in light of her opponent's recent struggles, will be fancy her chances of repeating the result on Monday afternoon.
 Sara Errani (ITA #7) vs.  Ana Ivanovic (SRB #17)
Head-to-head: Ivanovic leads 2-1
Sara Errani has barely broken sweat so far in Miami, defeating Daniela Hantuchova and Simona Halep for the loss of just five games. Her next test, against a similarly high-flying Ana Ivanovic, though, is likely to be somewhat tougher.
Ivanovic produced arguably her most impressive outing of the season against Svetlana Kuznetsova on Sunday night, striking her forehand and serve particularly well as she sauntered to victory. Tempering this optimism slightly will be her recent record against the WTA's elite; Ivanovic has to go back over a year for her last Top 10 win, losing nine on the spin in the intervening period.
Also on court?
World No.1 and five-time Miami champion Serena Williams takes on Dominika Cibulkova on Stadium, while later in the day fellow title favorite Maria Sharapova follows her on court against Klara Zakopalova.