Agnieszka Radwańska was the defending champion, but lost 6–0, 6–3 in the semifinals to the eventual champion Serena Williams.
Nadia Petrova was the defending champion, but she chose to compete in Eastbourne instead.
Simona Halep won the title beating in the final Kirsten Flipkens, 6–4, 6–2.
Li Na was the defending women's singles tournament champion, but lost to Serena Williams in the semifinals.
Serena Williams successfully defended her title, beating Li Na in the final, 7–5, 6–1. This was Williams' record seventh Miami title, and was Li's last tournament final before her retirement later in 2014.
Lucie Šafářová was the defending champion, but lost to Çağla Büyükakçay in the second round.
Simona Halep was the defending champion, but lost in the quarterfinals to Serena Williams.
Serena Williams was the two-time defending champion, but withdrew before the tournament began due to injury.
Victoria Azarenka was the defending champion, but did not participate this year as she was on maternity leave.
Simona Halep was the defending champion, but lost in the semifinals to Elina Svitolina.
Karolína Plíšková was the defending champion, but lost in the semifinals to Garbiñe Muguruza.
Agnieszka Radwańska was the defending champion, but lost in the semifinals to Daria Gavrilova.
Kristina Mladenovic was the defending champion, but lost in the final to unseeded Petra Kvitová, 1–6, 2–6. As a result, Kvitová became the first left-handed player to win a singles title in Russia. She was also the first wildcard to win the event.
Markéta Vondroušová was the defending champion, but lost in the second round to Elise Mertens.
Elina Svitolina was the defending champion, but lost to Sloane Stephens in the semifinals.
Garbiñe Muguruza was the defending champion, but lost in the second round to Lesia Tsurenko.
Daria Kasatkina was the defending champion, but lost in the first round to Dayana Yastremska.
Elise Mertens was the defending champion, but lost in the second round to Yulia Putintseva.
Madison Keys was the defending champion but lost in the second round to Ons Jabeur.
Ashleigh Barty defeated Jil Teichmann in the final, 6–3, 6–1, to win the women's singles title at the 2021 Cincinnati Masters and her first title at the tournament. Barty won the title without dropping a set. It was her fifth and last title of the season, her third WTA 1000 title, and her 13th career singles title overall on the WTA Tour.
This was the first edition of the event.
Kristina Mladenovic 
Yulia Putintseva 
