The 2021 Porto Open was a professional tennis tournament played on hard courts. It was the first edition of the tournament which was part of the 2021 ATP Challenger Tour. It took place in Porto, Portugal between 28 June and 4 July 2021.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Brazil | Thiago Seyboth Wild | 127 | 1 | |
 India | Prajnesh Gunneswaran | 147 | 2 | |
 Ecuador | Emilio Gómez | 171 | 3 | |
| Alejandro Tabilo | 174 | 4 | ||
| Frederico Ferreira Silva | 176 | 5 | ||
 Japan | Go Soeda | 177 | 6 | |
 Australia | Thanasi Kokkinakis | 182 | 7 | |
 Uzbekistan | Denis Istomin | 188 | 8 |
The following players received wildcards into the singles main draw:
The following players received entry into the singles main draw as alternates:
The following players received entry from the qualifying draw:
The following player received entry as a lucky loser:
See main article: 2021 Porto Open – Singles.
Altuğ Çelikbilek def. 
Quentin Halys 6–2, 6–1.See main article: 2021 Porto Open – Doubles.
Guido Andreozzi / Guillermo Durán def. Renzo Olivo / 
Miguel Ángel Reyes-Varela 6–7(5–7), 7–6(7–5), [11–9].
