| Singles | |
|---|---|
| 2018 Zagreb Ladies Open | |
| Champion |  Tereza Mrdeža |
| Runner-up |  Paula Ormaechea |
| Final score | 2–6, 6–4, 7–5 |
Dia Evtimova was the defending champion, having won the previous event in 2011, but chose not to participate.
Tereza Mrdeža won the title, defeating Paula Ormaechea in the final, 2–6, 6–4, 7–5.
Sabina Sharipova (first round)
Viktoriya Tomova (second round)
Georgina García Pérez (quarterfinals)
Valentini Grammatikopoulou (second round) Elitsa Kostova (second round)
Martina Di Giuseppe (first round)
Jana Čepelová (second round) Tereza Mrdeža (champion)| Semifinals | Final | ||||||||||||
 Alexandra Cadanțu | 2 | 1r | |||||||||||
| 8 | Tereza Mrdeža | 6 | 5 | ||||||||||
| 8 | Tereza Mrdeža | 2 | 6 | 7 | |||||||||
| Q | Paula Ormaechea | 6 | 4 | 5 | |||||||||
 Olga Doroshina | 5 | 4 | |||||||||||
| Q | Paula Ormaechea | 7 | 6 | ||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 | S Sharipova | 1 | 3 | ||||||||||||||||||||||||
| A Cadanțu | 6 | 6 | A Cadanțu | 6 | 6 | ||||||||||||||||||||||
| A Grymalska | 6 | 6 | A Grymalska | 2 | 2 | ||||||||||||||||||||||
 C Burger | 4 | 3 | A Cadanțu | 6 | 6 | ||||||||||||||||||||||
 P Özgen | 6 | 7 | P Özgen | 2 | 3 | ||||||||||||||||||||||
| Q |  C Lister | 3 | 5 | P Özgen | 6 | 6 | |||||||||||||||||||||
 D Seguel | 6 | 5 | 1r | 7 | J Čepelová | 3 | 3 | ||||||||||||||||||||
| 7 | J Čepelová | 4 | 7 | 4 | A Cadanțu | 2 | 1r | ||||||||||||||||||||
| 3 | G García Pérez | 1 | 77 | 6 | 8 | T Mrdeža | 6 | 5 | |||||||||||||||||||
| R Šramková | 6 | 65 | 4 | 3 | G García Pérez | 1 | 6 | 7 | |||||||||||||||||||
| WC |  A Husarić | 5 | 4 | WC |  B Jovanovski Petrović | 6 | 3 | 5 | |||||||||||||||||||
| WC | B Jovanovski Petrović | 7 | 6 | 3 | G García Pérez | 3 | 3 | ||||||||||||||||||||
| L Samsonova | 65 | 6 | 77 | 8 | T Mrdeža | 6 | 6 | ||||||||||||||||||||
| PR | A Panova | 77 | 3 | 65 | L Samsonova | 6 | 3 | 4 | |||||||||||||||||||
 D Gálfi | 3 | 1 | 8 | T Mrdeža | 4 | 6 | 6 | ||||||||||||||||||||
| 8 | T Mrdeža | 6 | 6 | ||||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 6 | M Di Giuseppe | 3 | 63 | ||||||||||||||||||||||||
 A Gámiz | 6 | 77 | A Gámiz | 3 | 2 | ||||||||||||||||||||||
| O Doroshina | 6 | 5 | 6 | O Doroshina | 6 | 6 | |||||||||||||||||||||
| M Hončová | 1 | 7 | 1 | O Doroshina | 6 | 0 | 6 | ||||||||||||||||||||
 M Georges | 4 | 1 |  K Juvan | 1 | 6 | 3 | |||||||||||||||||||||
| K Juvan | 6 | 6 | K Juvan | 6 | 6 | ||||||||||||||||||||||
| WC | L Bošković | 3 | 65 | 4 | V Grammatikopoulou | 3 | 2 | ||||||||||||||||||||
| 4 | V Grammatikopoulou | 6 | 77 | O Doroshina | 5 | 4 | |||||||||||||||||||||
| 5 | E Kostova | 6 | 6 | Q | P Ormaechea | 7 | 6 | ||||||||||||||||||||
| Q | Á Bukta | 3 | 4 | 5 | E Kostova | 6 | 2 | 3 | |||||||||||||||||||
| T Lukas | 7 | 7 | T Lukas | 1 | 6 | 6 | |||||||||||||||||||||
| WC | S Njirić | 5 | 5 | T Lukas | 5 | 7 | 1 | ||||||||||||||||||||
| Q | A Moratelli | 5 | 1 | Q | P Ormaechea | 7 | 5 | 6 | |||||||||||||||||||
| Q | P Ormaechea | 7 | 6 | Q | P Ormaechea | 5 | 6 | 6 | |||||||||||||||||||
| PR |  L Gjorcheska | 5 | 2 | 2 | V Tomova | 7 | 2 | 4 | |||||||||||||||||||
| 2 | V Tomova | 7 | 6 | ||||||||||||||||||||||||
Anabel Medina Garrigues was the defending champion, but lost to Maria Elena Camerin in the first round.
Iryna Brémond was the defending champion, but chose not to participate.
Alexandra Panova was the defending champion, but chose not to participate.
Lara Arruabarrena Vecino was the defending champion, but lost to Karin Knapp in the quarterfinals.
Jelena Janković won the title, defeating Paula Ormaechea in the final, 6–1, 6–2.
Tímea Babos was the defending champion, but lost in the quarterfinals to Monica Niculescu.
Olivia Rogowska was the defending champion, however she chose not to participate.
An-Sophie Mestach was the defending champion, but she chose to compete in Albuquerque instead.
Diāna Marcinkēviča was the defending champion, but she lost in qualifying.
Nicola Geuer and Anna Zaja were the defending champions, but Zaja chose not to participate. Geuer partnered Eva Wacanno, but they lost in the first round to Amina Anshba and Alina Silich.
Samantha Stosur was the defending champion but lost in the quarterfinals to Dominika Cibulková.
Anastasia Pavlyuchenkova was the defending champion, but chose to compete in Linz instead.
Estrella Cabeza Candela was the defending champion, but chose not to participate.
Anastasija Sevastova was the defending champion, but lost in the second round to Patricia Maria Țig.
Roberta Vinci was the champion the last time the tournament was held in 2013, but she has since retired from professional tennis.
Tereza Mrdeža was the defending champion, but lost in the second round to Anna Bondár.
Cristina Bucșa and María Fernanda Herazo were the defending champions, but Herazo chose not to participate. Bucșa partnered alongside Diāna Marcinkēviča, but lost in the quarterfinals to Lou Brouleau and Ioana Loredana Roșca.
Simona Halep was the defending champion, having won the previous edition in 2013, but chose not to participate.
Maryna Zanevska won her maiden WTA Tour singles title, defeating Kristína Kučová in the final, 6–4, 7–6(7–4).
The 2021 Karlsruhe Open was a professional tennis tournament played on outdoor clay courts. It was the 2nd edition of the tournament and part of the 2021 WTA 125K series, offering a total of $125,000 in prize money. It took place in Karlsruhe, Germany between 7 and 12 September 2021. The tournament did not take place in 2020 due to the COVID-19 pandemic. The singles part of the tournament had 32 competitors. Patricia Maria Țig was the defending champion, having won the previous edition in 2019, but chose not to participate. Mayar Sherif won the title, defeating Martina Trevisan in the final, 6–3, 6–2.
Anna Chakvetadze was the champion when the event was last held in 2010, but she retired from professional tennis in 2013.