The 15-year-old American beat Zarina Diyas, 6-2, 6-1.
The Belarusian was No. 1 back in 2012 after winning the Australian Open.
The former No. 7 won her first WTA match in four years in Miami before losing to Simona Halep.
The Argentine fell to Vasek Pospisil, 6-4, 7-6 (7).
The American leads their head-to-head 17-2, and hasn't lost to the Russian since 2004.
Previewing and predicting the men's draw at the Miami Open.
Capturing and captioning the singles and doubles finals at the BNP Paribas Open.
After years of self-sabotage and neglect, Bernard Tomic is considering his place in the sport.
Four years after a setback, 34-year-old Venus Williams continues to turn back the clock.