| Singles | |
|---|---|
| 2021 Portugal Ladies Open | |
| Champion |  Zheng Saisai |
| Runner-up |  Harmony Tan |
| Score | 6–4, 3–6, 6–3 |
Isabella Shinikova was the defending champion [1] but chose to compete at the 2021 BGL Luxembourg Open instead.
Zheng Saisai won the title, defeating Harmony Tan in the final, 6–4, 3–6, 6–3.
Zheng Saisai Wang Xinyu (quarterfinals) Harmony Tan (final)
Maddison Inglis (semifinals) Arina Rodionova (first round) Lizette Cabrera (first round)
Beatriz Haddad Maia (semifinals)
Daria Snigur (first round)| Semifinals | Final | ||||||||||||
| 1 | Zheng Saisai | 6 | 6 | ||||||||||
| 4 | Maddison Inglis | 2 | 3 | ||||||||||
| 1 | Zheng Saisai | 6 | 3 | 6 | |||||||||
| 3 | Harmony Tan | 4 | 6 | 3 | |||||||||
| 3 | Harmony Tan | 77 | 77 | ||||||||||
| 7 | Beatriz Haddad Maia | 65 | 64 | ||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 | S Zheng | 6 | 6 | ||||||||||||||||||||||||
 K Okamura | 2 | 1 | 1 | S Zheng | 2 | 7 | 7 | ||||||||||||||||||||
| A Hesse | 6 | 6 | A Hesse | 6 | 5 | 5 | |||||||||||||||||||||
| C Monnet | 1 | 4 | 1 | S Zheng | 6 | 6 | |||||||||||||||||||||
 M Benoît | 6 | 6 | M Benoît | 3 | 1 | ||||||||||||||||||||||
| WC |  S Lança | 2 | 0 | M Benoît | 4 | 6 | 6 | ||||||||||||||||||||
| Q |  IL Roșca | 4 | 6 | 77 | Q | IL Roșca | 6 | 4 | 4 | ||||||||||||||||||
| 6 | L Cabrera | 6 | 3 | 64 | 1 | S Zheng | 6 | 6 | |||||||||||||||||||
| 4 | M Inglis | 3 | 7 | 6 | 4 | M Inglis | 2 | 3 | |||||||||||||||||||
| Q |  W Falkowska | 6 | 5 | 3 | 4 | M Inglis | 6 | 6 | |||||||||||||||||||
 R Anderson | 77 | 3 | 5 |  N Stevanović | 2 | 1 | |||||||||||||||||||||
| N Stevanović | 63 | 6 | 7 | 4 | M Inglis | 6 | 4 | 6 | |||||||||||||||||||
| Q | O Gadecki | 4 | 6 | 6 | SE |  A Kulikova | 2 | 6 | 3 | ||||||||||||||||||
| WC |  D Spiteri | 6 | 1 | 1 | Q | O Gadecki | 6 | 4 | 4 | ||||||||||||||||||
| SE | A Kulikova | 6 | 6 | SE | A Kulikova | 2 | 6 | 6 | |||||||||||||||||||
| 5 | Ar Rodionova | 0 | 4 | ||||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 8/JE | D Snigur | 3 | 4 | ||||||||||||||||||||||||
| J Ponchet | 6 | 6 | J Ponchet | 5 | 4 | ||||||||||||||||||||||
| WC | I Murta | 3 | 3 | Q |  R Șerban | 7 | 6 | ||||||||||||||||||||
| Q | R Șerban | 6 | 6 | Q | R Șerban | 64 | 5 | ||||||||||||||||||||
| WC | F Jorge | 6 | 66 | 6 | 3 | H Tan | 77 | 7 | |||||||||||||||||||
| C Alves | 2 | 78 | 2 | WC | F Jorge | 2 | 2 | ||||||||||||||||||||
| Q | S Djoubri | 3 | 3 | 3 | H Tan | 6 | 6 | ||||||||||||||||||||
| 3 | H Tan | 6 | 6 | 3 | H Tan | 77 | 77 | ||||||||||||||||||||
| 7 | B Haddad Maia | 6 | 6 | 7 | B Haddad Maia | 65 | 64 | ||||||||||||||||||||
| Q |  E Silva | 0 | 1 | 7 | B Haddad Maia | 6 | 6 | ||||||||||||||||||||
| E Perez | 6 | 6 | E Perez | 4 | 4 | ||||||||||||||||||||||
| Q |  S-R Sekulic | 2 | 2 | 7 | B Haddad Maia | 6 | 6 | ||||||||||||||||||||
| T Maria | 6 | 6 | 2 | Xin Wang | 3 | 4 | |||||||||||||||||||||
| Q | E Bogdan | 2 | 4 | T Maria | 2 | 1 | |||||||||||||||||||||
 A Tikhonova | 3 | 5 | 2 | Xin Wang | 6 | 6 | |||||||||||||||||||||
| 2 | Xin Wang | 6 | 7 | ||||||||||||||||||||||||
Serena Williams was the defending champion, and successfully defended her title, defeating lucky loser CoCo Vandeweghe in the final, 7–5, 6–3. It was the first all-American final on the WTA Tour since the 2009 WTA Tour Championships, and the first on American soil since Los Angeles in 2004.
Wang Qiang was the defending champion, having won the event in 2012, but lost in the first round to Wang Yafan.
The tournament in Nanchang was a new addition to the WTA 125K series.
Monica Niculescu and Klára Koukalová were the defending champions, but Koukalová chose not to participate.
Niculescu partnered Vitalia Diatchenko, but lost in the final to Kiki Bertens and Johanna Larsson, 5–7, 3–6.
Zheng Saisai was the defending champion, and successfully defended her title, defeating Han Xinyun in the all-Chinese final, 6–4, 3–6, 6–4.
This was a new event to the WTA 125K series.
Alla Kudryavtseva and Anastasia Rodionova were the defending champions, but chose not to participate.
Lyudmyla Kichenok and Nadiia Kichenok were the defending champions, but chose to participate in Auckland instead.
Vania King and Monica Niculescu won the title, defeating Xu Yifan and Zheng Saisai in the final, 6–1, 6–4.
Chang Kai-chen and Zheng Saisai were the defending champions, but Zheng chose not to participate this year. Chang played alongside Duan Yingying, but lost in the first round to Nicha Lertpitaksinchai and Peangtarn Plipuech.
Chan Hao-ching and Chan Yung-jan were the defending champions, but decided not to participate this year.
Shuko Aoyama and Makoto Ninomiya won the title, defeating Jocelyn Rae and Anna Smith in the final, 6–3, 6–3.
Olga Govortsova was the defending champion, but chose not to participate.
Zheng Saisai was the defending champion, and successfully defended her title, defeating Liu Fangzhou in the final, 6–3, 6–1.
Zheng Saisai was the defending champion but lost in the final to Irina Khromacheva 3–6, 6–4, 7–6(7–5).
Donna Vekić was the defending champion, but lost in the semifinals to Johanna Konta in a rematch of the previous year's final.
Carol Zhao was the defending champion, but lost to Ivana Jorović in the quarterfinals.
Mihaela Buzărnescu was the defending champion, but lost to Daria Kasatkina in the first round.
Hsieh Su-wei and Barbora Strýcová were the defending champions and successfully defended their title, defeating Barbora Krejčíková and Zheng Saisai in the final, 7–5, 3–6, [10–5].
María Camila Osorio Serrano defeated Tamara Zidanšek in the final, 5–7, 6–3, 6–4, to win the singles tennis title at the 2021 Copa Colsanitas. It was the Colombian teenage wildcard's first career Women's Tennis Association (WTA) singles title. Ranked No. 180, Osorio Serrano became the lowest-ranked WTA title holder since world No. 299 Margarita Gasparyan at the 2018 Tashkent Open. Zidanšek was also in contention for her first WTA title.
Sorana Cîrstea defeated Elise Mertens in the final, 6–1, 7–6(7–3) to win the women's singles tennis title at the 2021 İstanbul Cup. This was Cîrstea's first title since 2008. Cîrstea did not drop a set throughout the tournament.
Zheng Saisai was the reigning champion but chose not to participate.