2021 Western & Southern Open – Women's singles

Ashleigh Barty defeated Jil Teichmann in the final, 6–3, 6–1 to win the women's singles tennis title at the 2021 Cincinnati Masters. Barty did not drop a set en route to her first Cincinnati Masters title. It was her fifth and last title of the season, her third WTA 1000 title, and her 13th career WTA Tour singles title.

Victoria Azarenka was the defending champion, but lost in the third round to Barty.

Angelique Kerber contested her 1000th match in her professional career in the quarterfinals against Petra Kvitová; she won the match after Kvitová retired.

This was the final tournament in which former world No. 4 and British No. 1 Johanna Konta competed before her retirement. She was defeated in the first round by Karolína Muchová.

Seeds
The top eight seeds received a bye into the second round. • 🇦🇺 Ashleigh Barty (champion)

• 🇯🇵 Naomi Osaka (third round)

• 🇧🇾 Aryna Sabalenka (second round)

• 🇺🇦 Elina Svitolina (second round)

• 🇨🇿 Karolína Plíšková (semifinals)

• 🇵🇱 Iga Świątek (second round)

• 🇨🇦 Bianca Andreescu (second round)

• 🇪🇸 Garbiñe Muguruza (third round)

• 🇨🇿 Barbora Krejčíková (quarterfinals)

• Belinda Bencic (quarterfinals)

• 🇨🇿 Petra Kvitová (quarterfinals, retired)

• 🇷🇴 Simona Halep (second round, withdrew)

• 🇺🇸 Jennifer Brady (second round, retired)

• 🇧🇾 Victoria Azarenka (third round)

• 🇧🇪 Elise Mertens (second round)

• 🇷🇺 Anastasia Pavlyuchenkova (withdrew)

Seeds
• # Viktorija Golubic (first round)

• # 🇨🇳 Zhang Shuai (qualified)

• # 🇷🇺 Liudmila Samsonova (qualified)

• # 🇸🇪 Rebecca Peterson (qualifying competition, lucky loser)

• # 🇨🇿 Kateřina Siniaková (withdrew)

• # Donna Vekić (qualifying competition)

• # 🇫🇷 Kristina Mladenovic (first round)

• # 🇨🇿 Tereza Martincová (first round)

• # 🇫🇷 Caroline Garcia (qualified)

• # Anastasija Sevastova (first round, retired)

• # 🇬🇧 Heather Watson (qualified)

• # 🇩🇪 Andrea Petkovic (qualifying competition)

• # 🇨🇦 Leylah Annie Fernandez (qualified)

• # Hsieh Su-wei (qualified)

• # 🇨🇿 Marie Bouzková (qualifying competition)

• # 🇨🇴 Camila Osorio (first round)

Qualifiers
• # 🇫🇷 Caroline Garcia

• # 🇨🇳 Zhang Shuai

• # 🇷🇺 Liudmila Samsonova

• # 🇬🇧 Heather Watson

• # Hsieh Su-wei

• # 🇮🇹 Jasmine Paolini

• # 🇧🇾 Aliaksandra Sasnovich

• # 🇨🇦 Leylah Annie Fernandez

Lucky loser
• # 🇸🇪 Rebecca Peterson