| Doubles | |
|---|---|
| 2021 Croatia Open Umag | |
| Champions |  Fernando Romboli  David Vega Hernández |
| Runners-up |  Tomislav Brkić  Nikola Ćaćić |
| Score | 6–3, 7–5 |
Robin Haase and Philipp Oswald were the reigning champions from when the tournament was last held in 2019, [1] but chose not to defend their title.
Fernando Romboli and David Vega Hernández won the title, defeating Tomislav Brkić and Nikola Ćaćić in the final, 6–3, 7–5. [2]
Tomislav Brkić / Nikola Ćaćić (final)
Pablo Cuevas / 
Fabrice Martin (first round) Rafael Matos / 
Andrei Vasilevski (first round)
Luis David Martínez / 
Artem Sitak (first round)| First round | Quarterfinals | Semifinals | Final | ||||||||||||||||||||||||
| 1 | T Brkić N Ćaćić | 6 | 3 | [10] | |||||||||||||||||||||||
| WC |  D Ajduković F Ninčević | 4 | 6 | [8] | 1 | T Brkić N Ćaćić | 6 | 6 | |||||||||||||||||||
 R Jebavý J Veselý | 7 | 6 | R Jebavý J Veselý | 2 | 2 | ||||||||||||||||||||||
| C Taberner B Zapata Miralles | 5 | 3 | 1 | T Brkić N Ćaćić | 6 | 6 | |||||||||||||||||||||
| 4 | LD Martinez A Sitak | 6 | 61 | [6] | I Sabanov M Sabanov | 1 | 2 | ||||||||||||||||||||
| I Sabanov M Sabanov | 3 | 77 | [10] | I Sabanov M Sabanov | 7 | 6 | |||||||||||||||||||||
 S Caruso G Mager | 78 | 2 | [6] | D Džumhur A Šančić | 5 | 0 | |||||||||||||||||||||
| D Džumhur A Šančić | 66 | 6 | [10] | 1 | T Brkić N Ćaćić | 3 | 5 | ||||||||||||||||||||
 R Albot P Martínez | 6 | 77 | F Romboli D Vega Hernández | 6 | 7 | ||||||||||||||||||||||
 A Begemann  I Zelenay | 4 | 65 | R Albot P Martínez | 6 | 6 | ||||||||||||||||||||||
| M Cecchinato S Travaglia | 7 | 6 | M Cecchinato S Travaglia | 4 | 1 | ||||||||||||||||||||||
| 3 | R Matos A Vasilevski | 5 | 4 | R Albot P Martínez | 6 | 68 | [7] | ||||||||||||||||||||
| PR | M López J Munar | 5 | 6 | [5] | F Romboli D Vega Hernández | 4 | 710 | [10] | |||||||||||||||||||
| F Romboli D Vega Hernández | 7 | 4 | [10] | F Romboli D Vega Hernández | 3 | 7 | [16] | ||||||||||||||||||||
| WC | A Kalender M Poljičak | 6 | 6 | WC | A Kalender M Poljičak | 6 | 5 | [14] | |||||||||||||||||||
| 2 | P Cuevas F Martin | 3 | 4 | ||||||||||||||||||||||||
Fernando Romboli de Souza is a Brazilian professional tennis player who specializes in doubles. He reached his highest ATP doubles ranking of world No. 88, on 18 July 2022 and his highest singles ranking of No. 236, on 20 June 2011. Romboli won the ATP 250 doubles title in 2021 Croatia Open alongside Spaniard David Vega Hernández. He competes mainly on the ATP Challenger Tour where he has won 20 doubles titles.
David Vega Hernández is a Spanish professional tennis player. He has a career-high ATP doubles ranking of world No. 28 achieved on 21 July 2014. He also has a career high ATP singles ranking of No. 403 achieved on 13 February 2023. Hernández has won five ATP Tour doubles titles. He competes mainly on the ATP Challenger Tour where he has won 13 doubles titles.
Mateusz Kowalczyk and Andreas Mies were the defending champions but chose not to defend their title.
Salvatore Caruso and Jonathan Eysseric were the defending champions but chose not to defend their title.
Kevin Krawietz and Andreas Mies were the defending champions but chose not to defend their title.
Denys Molchanov and Igor Zelenay were the defending champions but chose not to defend their title.
Filippo Baldi and Andrea Pellegrino were the defending champions but chose not to defend their title.
Fabrício Neis and David Vega Hernández were the defending champions but only Vega Hernández chose to defend his title, partnering Fernando Romboli. Vega Hernández lost in the quarterfinals to Eduard Esteve Lobato and Oriol Roca Batalla.
Sander Gillé and Joran Vliegen were the defending champions but chose not to defend their title.
This was the first edition of the tournament.
This was the first edition of the tournament, primarily organised due to the cancellation of some tournaments in 2021, due to the COVID-19 pandemic.
The 2021 Croatia Open is a men's tennis tournament played on outdoor clay courts. It is the 31st edition of the Croatia Open, and part of the 250 Series of the 2021 ATP Tour. It take place at the International Tennis Center in Umag, Croatia, from 19 through 25 July 2021.
Robert Lindstedt and Jan-Lennard Struff were the reigning champions from when the tournament was last held in 2019, but chose not to participate this year.
Jamie Murray and Neal Skupski were the defending champions, but chose to compete in San Diego with different partners instead.
Marcelo Demoliner and Matwé Middelkoop were the reigning champions from when the tournament was last held in 2019, but chose to compete with different partners. Demoliner played alongside Marcus Daniell, but lost in the first round to Ariel Behar and Gonzalo Escobar.
Tomislav Brkić and Nikola Ćaćić were the defending champions but lost in the semifinals to Santiago González and Andrés Molteni.
Tomislav Brkić and Francisco Cabral defeated Robin Haase and Philipp Oswald in the final, 6–4, 6–4 to win the doubles tennis title at the 2022 Swiss Open Gstaad.
Simone Bolelli and Fabio Fognini defeated Lloyd Glasspool and Harri Heliövaara in the final, 5–7, 7–6(8–6), [10–7] to win the doubles tennis title at the 2022 Croatia Open Umag. The Italians saved six match points in the second-set tie-break from 0–6 down.
This was the first edition of the tournament.
Dominic Stricker and Stan Wawrinka defeated Marcelo Demoliner and Matwé Middelkoop in the final, 7–6(10–8), 6–2 to win the doubles tennis title at the 2023 Swiss Open Gstaad. This was the first doubles final and title in ten and a half years for Wawrinka.