| Singles | |
|---|---|
| 2021 Iași Open | |
| Champion |  Zdeněk Kolář |
| Runner-up |  Hugo Gaston |
| Score | 7–5, 4–6, 6–4 |
Carlos Taberner was the defending champion [1] but chose not to defend his title.
Zdeněk Kolář won the title after defeating Hugo Gaston 7–5, 4–6, 6–4 in the final.
Hugo Gaston (final) Enzo Couacaud (first round) Alexandre Müller (first round)
Felipe Meligeni Alves (semifinals) Zdeněk Kolář (champion)
Marius Copil (second round) Maxime Janvier (first round)
Dimitar Kuzmanov (quarterfinals)| Semifinals | Final | ||||||||||||
| 1 | Hugo Gaston | 7 | 77 | ||||||||||
| 4 | Felipe Meligeni Alves | 5 | 64 | ||||||||||
| 1 | Hugo Gaston | 5 | 6 | 4 | |||||||||
| 5 | Zdeněk Kolář | 7 | 4 | 6 | |||||||||
| Q |  Miljan Zekić | 5 | 6 | 2 | |||||||||
| 5 | Zdeněk Kolář | 7 | 2 | 6 | |||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 | H Gaston | 6 | 3 | 6 | |||||||||||||||||||||||
 N Fatić | 1 | 6 | 1 | 1 | H Gaston | 4 | 6 | 77 | |||||||||||||||||||
 M Pecotić | 4 | 6 | 6 | M Pecotić | 6 | 4 | 65 | ||||||||||||||||||||
 R Ortega Olmedo | 6 | 0 | 1 | 1 | H Gaston | 77 | 6 | ||||||||||||||||||||
| D Ajduković | 6 | 6 | D Ajduković | 64 | 2 | ||||||||||||||||||||||
| WC | C Crețu | 3 | 2 | D Ajduković | 6 | 6 | |||||||||||||||||||||
| Q | A Lazarov | 6 | 3 | 2 | 6 | M Copil | 4 | 4 | |||||||||||||||||||
| 6 | M Copil | 3 | 6 | 6 | 1 | H Gaston | 7 | 77 | |||||||||||||||||||
| 4 | F Meligeni Alves | 7 | 6 | 4 | F Meligeni Alves | 5 | 64 | ||||||||||||||||||||
 I Sijsling | 5 | 2 | 4 | F Meligeni Alves | 6 | 6 | |||||||||||||||||||||
| WC | Ștefan Paloși | 4 | 4 | PR |  M Donati | 3 | 3 | ||||||||||||||||||||
| PR | M Donati | 6 | 6 | 4 | F Meligeni Alves | 6 | 3 | 6 | |||||||||||||||||||
| N Sánchez Izquierdo | 3 | 6 | 2 | 8 | D Kuzmanov | 0 | 6 | 3 | |||||||||||||||||||
| WC | ND Ionel | 6 | 4 | 6 | WC | ND Ionel | 6 | 3 | 4 | ||||||||||||||||||
| P Krstin | 2 | 2 | 8 | D Kuzmanov | 2 | 6 | 6 | ||||||||||||||||||||
| 8 | D Kuzmanov | 6 | 6 | ||||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 7 | M Janvier | 3 | 64 | ||||||||||||||||||||||||
| Q | M Zekić | 6 | 77 | Q | M Zekić | 6 | 77 | ||||||||||||||||||||
| Alt |  H Casanova | 6 | 6 | Alt | H Casanova | 3 | 63 | ||||||||||||||||||||
| N Serdarušić | 4 | 4 | Q | M Zekić | 7 | 6 | |||||||||||||||||||||
 T Gabashvili | 5 | 6 | 5 |  L Miedler | 5 | 2 | |||||||||||||||||||||
| L Miedler | 7 | 4 | 7 | L Miedler | 77 | 6 | |||||||||||||||||||||
| A Andreev | 6 | 1 | 6 | A Andreev | 65 | 1 | |||||||||||||||||||||
| 3 | A Müller | 4 | 6 | 3 | Q | M Zekić | 5 | 6 | 2 | ||||||||||||||||||
| 5 | Z Kolář | 6 | 7 | 5 | Z Kolář | 7 | 2 | 6 | |||||||||||||||||||
| Q | David Poljak | 2 | 5 | 5 | Z Kolář | 6 | 6 | ||||||||||||||||||||
 A Dougaz | 6 | 77 | A Dougaz | 2 | 3 | ||||||||||||||||||||||
| LL | B Bobrov | 4 | 64 | 5 | Z Kolář | 6 | 6 | ||||||||||||||||||||
| Q | Dan Alexandru Tomescu | 4 | 3 | R Bonadio | 4 | 4 | |||||||||||||||||||||
| FC Jianu | 6 | 6 | FC Jianu | 65 | 2 | ||||||||||||||||||||||
| R Bonadio | 77 | 6 | R Bonadio | 77 | 6 | ||||||||||||||||||||||
| 2 | E Couacaud | 65 | 3 | ||||||||||||||||||||||||
Andre Begemann and Aliaksandr Bury were the defending champions but chose not to defend their title.
Tuna Altuna and Václav Šafránek were the defending champions but only Altuna chose to defend his title, partnering Elias Ymer. Altuna lost in the first round to Julio Peralta and Horacio Zeballos.
David Ferrer was the defending champion, but lost in the second round to Casper Ruud.
Jannik Sinner was the defending champion but chose not to defend his title.
Andre Begemann and Daniel Masur were the defending champions but chose to defend their title with different partners. Begemann partnered Albano Olivetti but lost in the semifinals to Lloyd Glasspool and Harri Heliövaara. Masur partnered Julian Lenz but lost in the semifinals to Zdeněk Kolář and Andrea Vavassori.
Quentin Halys and Tristan Lamasine were the defending champions but only Halys chose to defend his title, partnering Lucas Pouille. Halys lost in the quarterfinals to Purav Raja and Tristan-Samuel Weissborn.
Oscar Otte was the defending champion but retired in the quarterfinals to Elias Ymer.
Zdeněk Kolář and Lukáš Rosol were the defending champions but only Kolář chose to defend his title, partnering Roman Jebavý. Kolář lost in the final to Aleksandr Nedovyesov and Gonçalo Oliveira.
Rafael Matos and João Menezes were the defending champions but chose not to defend their title.
Tommy Robredo was the defending champion but chose not to defend his title.
Zdeněk Kolář and Julian Ocleppo were the defending champions but only Kolář chose to defend his title, partnering Jiří Lehečka.
Zdeněk Kolář and Andrea Vavassori were the defending champions but chose not to defend their title.
Max Purcell and Luke Saville were the defending champions but chose not to compete.
Lucas Pouille was the defending champion but lost in the first round to Martín Cuevas.
Zdeněk Kolář was the defending champion but retired from his first round match with Frederico Ferreira Silva.
Dustin Brown and Andrea Vavassori were the defending champions but only Brown chose to defend his title, partnering Evan King. Brown lost in the first round to Lukáš Klein and Igor Zelenay.
Zdeněk Kolář was the defending champion but chose not to defend his title.
Quentin Halys was the defending champion but chose not to defend his title.
Felipe Meligeni Alves was the defending champion but chose not to defend his title.
Francesco Passaro was the defending champion but lost in the final to Hugo Gaston.