Before each day's play at the 2021 Miami Open, we'll preview three matches to look out for.
 Stefanos Tsitsipas vs.  Kei Nishikori
It’s been nearly two and a half years since these two went to battle for the first time. Nishikori took that meeting on home soil in Tokyo, but the landscape is significantly different these days. Tsitsipas has reached three Grand Slam semifinals and triumphed at the ATP Finals to become a mainstay in the Top 10. Nishikori, who ended the 2018 season ranked No. 9, has dipped 30 places following right elbow surgery in October 2019.
However, after a positive COVID-19 test last summer and 0-3 start to 2021, the 2014 US Open runner-up is finding his rhythm. In March, Nishikori has posted quality wins over Felix Auger-Aliassime, Alex de Minaur and David Goffin, and Saturday found his way past Aljaz Bedene for the second straight event. Tsitsipas hasn’t let up much since ousting Rafael Nadal in the Australian Open quarterfinals, advancing to the Rotterdam semifinals before coming up just short in the Acapulco title match to Alexander Zverev. Nishikori progressed to the quarterfinals or better four years in a row from 2014-2017, anchored by a 2016 final showing. Is he primed to win this third-round clash for his first Top 5 win since beating No. 3 Roger Federer at The O2 in November 2018?
 Ashleigh Barty vs.  Victoria Azarenka
All three of Azarenka’s wins over a No. 1-ranked player have come against Serena Williams when the American held the top spot. Azarenka and Barty know each other’s games well, not based on prior encounters but rather their numerous experiences as doubles partners in 2019. With Barty’s champion points dropping off as a result of the recently announced WTA ranking system adjustments, the No. 14 seed has a chance to greatly assist Naomi Osaka—winner of the past two majors including the US Open final over Azarenka—in her quest to wrestle the top spot away from the Australian.
Azarenka loves everything about this event, from the conditions to the scene of the host city. The Belarusian enters this showdown on the back of defeating Angelique Kerber for the ninth time in 10 tries. After winning from match point down against Kristina Kucova in the second round, Barty shook off her rust to dispatch Jelena Ostapenko with plenty of margin. Will her undefeated record at Hard Rock Stadium have any weight, or is Azarenka’s storied history at the South Florida event ready for another uplifting chapter?
 Bianca Andreescu vs.  Garbiñe Muguruza
Can Muguruza be stopped? With her comeback victory over Anna Kalinskaya Sunday, the two-time major champion has reeled off eight consecutive wins—and is on an 11-1 tear since missing out on two match points against eventual champion Osaka in the round of 16 at the Australian Open. Historically, Muguruza has lost all five of her previous fourth-round matches in Miami, a trend Andreescu hopes plays into her favor.
With six wins over eight matches played since returning from a 13-month layoff brought on by a right knee injury, street fighter Andreescu could possess the answer to the Muguruza riddle. In 2019, her wide-ranging toolbox befuddled the Spaniard, as Andreescu conceded just one game in a 52-minute thrashing en route to her breakthrough title run at Indian Wells. Will the 20-year-old capitalize on the final hard-court tournament before the WTA tour transitions to clay? An efficient break point conversion rate, after going just three for 17 against Amanda Anisimova in a grueling three-setter Sunday evening, would go a long way.