| Singles | |
|---|---|
| 2021 Rafa Nadal Open | |
| Champion |  Lukáš Lacko |
| Runner-up |  Yasutaka Uchiyama |
| Score | 5–7, 7–6(10–8), 6–1 |
Emil Ruusuvuori was the defending champion [1] but chose not to defend his title.
Lukáš Lacko won the title after defeating Yasutaka Uchiyama 5–7, 7–6(10–8), 6–1 in the final.
Yasutaka Uchiyama (final)
Fernando Verdasco (quarterfinals)
Liam Broady (first round)
João Sousa (quarterfinals)
Sebastian Ofner (second round, retired)
Marcelo Tomás Barrios Vera (second round)
Kacper Żuk (first round)
Blaž Rola (first round)| Semifinals | Final | ||||||||||||
| 1 | Yasutaka Uchiyama | 4 | 6 | 7 | |||||||||
| Q |  Michael Geerts | 6 | 1 | 5 | |||||||||
| 1 | Yasutaka Uchiyama | 7 | 68 | 1 | |||||||||
| Lukáš Lacko | 5 | 710 | 6 | ||||||||||
| Lukáš Lacko | 6 | 6 | |||||||||||
 Tobias Kamke | 0 | 3 | |||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 | Y Uchiyama | 4 | 3 | ||||||||||||||||||||||||
 S Diez | 6 | 3r | 1 | Y Uchiyama | 6 | 6 | |||||||||||||||||||||
| Q |  A González | 77 | 61 | 4 | LL | J Zieliński | 1 | 2 | |||||||||||||||||||
| LL | J Zieliński | 65 | 77 | 6 | 1 | Y Uchiyama | 4 | 6 | 77 | ||||||||||||||||||
 R Ramanathan | 61 | 6 | 7 | R Ramanathan | 6 | 4 | 65 | ||||||||||||||||||||
| WC | C Gómez-Herrera | 77 | 4 | 5 | R Ramanathan | 7 | 0 | ||||||||||||||||||||
| Alt |  R Quiroz | 77 | 3 | 2 | 5 | S Ofner | 5 | 0r | |||||||||||||||||||
| 5 | S Ofner | 65 | 6 | 6 | 1 | Y Uchiyama | 4 | 6 | 7 | ||||||||||||||||||
| 4 | J Sousa | 6 | 1 | 7 | Q | M Geerts | 6 | 1 | 5 | ||||||||||||||||||
| Alt | H Moriya | 4 | 6 | 5 | 4 | J Sousa | 6 | 6 | |||||||||||||||||||
| Alt | R Ortega Olmedo | 7 | 7 | Alt | R Ortega Olmedo | 3 | 3 | ||||||||||||||||||||
| Alt | N Mejía | 5 | 5 | 4 | J Sousa | 6 | 3 | 4 | |||||||||||||||||||
| Q | M Geerts | 4 | 6 | 6 | Q | M Geerts | 2 | 6 | 6 | ||||||||||||||||||
| T Ito | 6 | 2 | 1 | Q | M Geerts | 4 | 6 | 6 | |||||||||||||||||||
| WC | N Álvarez Varona | 4 | 63 | 6 | MT Barrios Vera | 6 | 2 | 1 | |||||||||||||||||||
| 6 | MT Barrios Vera | 6 | 77 | ||||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 7 | K Żuk | 3 | 4 | ||||||||||||||||||||||||
 D Kuzmanov | 6 | 6 | D Kuzmanov | 2 | 69 | ||||||||||||||||||||||
| Q | J Härteis | 2 | 3 | L Lacko | 6 | 711 | |||||||||||||||||||||
| L Lacko | 6 | 6 | L Lacko | 7 | 7 | ||||||||||||||||||||||
 B Tomic | 3 | 1 | F Ferreira Silva | 5 | 5 | ||||||||||||||||||||||
| F Ferreira Silva | 6 | 6 | F Ferreira Silva | 3 | 7 | 6 | |||||||||||||||||||||
 M Viola | 6 | 3 | 6 | M Viola | 6 | 5 | 0 | ||||||||||||||||||||
| 3 | L Broady | 4 | 6 | 4 | L Lacko | 6 | 6 | ||||||||||||||||||||
| 8 | B Rola | 4 | 4 | T Kamke | 0 | 3 | |||||||||||||||||||||
| T Kamke | 6 | 6 | T Kamke | 6 | 6 | ||||||||||||||||||||||
| Q |  N Chappell | 6 | 6 | Q | N Chappell | 2 | 4 | ||||||||||||||||||||
| Alt |  E Karlovskiy | 3 | 1 | T Kamke | 6 | 6 | |||||||||||||||||||||
| WC | D Rincón | 3 | 6 | 1 | 2 | F Verdasco | 3 | 1 | |||||||||||||||||||
| Alt | S Kozlov | 6 | 1 | 6 | Alt | S Kozlov | 6 | 66 | 2 | ||||||||||||||||||
| LL | N Moreno de Alboran | 3 | 2 | 2 | F Verdasco | 1 | 78 | 6 | |||||||||||||||||||
| 2 | F Verdasco | 6 | 6 | ||||||||||||||||||||||||
Daniel Berta was the defending champion, but he lost in the first round against Junior A. Ore.
Agustín Velotti won the title after defeating Andrea Collarini in the final, 6–4, 7–5.
Teymuraz Gabashvili was the defending champion, but decided not to compete.
Blaž Kavčič was the defending champion, but elected not to defend his title.
Hyeon Chung clinched his maiden ATP Challenger Tour title, beating Jordan Thompson 7–6(7–0), 6–4 in the final.
Kei Nishikori was the defending champion but chose not to participate this year. Three-time losing finalist Julien Benneteau did not participate either.
Yūichi Sugita was the defending champion but lost in the quarterfinals to Lloyd Harris.
Go Soeda was the defending champion but chose not to defend his title.
Frances Tiafoe was the defending champion but chose not to defend his title.
Marcel Granollers and Marcin Matkowski were the defending champions, but Granollers chose to compete in Beijing instead. Matkowski played alongside Aisam-ul-Haq Qureshi, but lost in the first round to Santiago González and Julio Peralta.
Yasutaka Uchiyama was the defending champion but lost in the first round to Michał Przysiężny.
Yūichi Sugita was the defending champion but chose not to defend his title.
Ben McLachlan and Yasutaka Uchiyama were the defending champions but chose not to participate together. McLachlan played alongside Jan-Lennard Struff and successfully defended the title, defeating Raven Klaasen and Michael Venus in the final, 6–4, 7–5. Uchiyama teamed up with Joe Salisbury, but lost in the semifinals to Klaasen and Venus.
Peter Polansky was the defending champion but lost in the semifinals to Yasutaka Uchiyama.
Alexei Popyrin was the defending champion but chose not to defend his title.
Blaž Kavčič was the defending champion but chose not to defend his title.
Rogério Dutra Silva was the defending champion but chose not to defend his title.
Roger Federer was the defending champion, but withdrew from the tournament after undergoing surgery on his right knee.
First seed Alexander Zverev won the tournament, defeating third seed Félix Auger-Aliassime 6–3, 6–3 in the final. This was the first edition of the tournament, primarily organised due to the cancellation of many tournaments in 2020, due to the COVID-19 pandemic.
Andy Murray was the defending champion, but this year he decided to participate in the Cologne event instead, where he later withdrew due to hip injury.
Dennis Novak was the defending champion but chose not to defend his title.
Jenson Brooksby was the defending champion but withdrew from the quarterfinals.