2021 Miami Open – Women's singles
Ashleigh Barty was the defending champion from when the tournament was last held in 2019, and she successfully defended her title after Bianca Andreescu retired from the final with the scoreline at 6–3, 4–0. Barty saved a match point in the second round against Kristína Kučová en route to the title. The victory earned Barty her first successful title defense in her singles career and made her the sixth woman to accomplish a title defense at the Miami Open. Barty and Naomi Osaka were in contention for the WTA No. 1 singles ranking at  the beginning of the tournament. After Osaka lost to Maria Sakkari in the quarterfinals, which snapped a 23-match winning streak that dated back to the 2020 Cincinnati Masters, Barty retained the top ranking after winning the title. Seeds. All seeds received a bye into the second round.