| Coupe Davis | 09/15 02:00 | 26 | [42] Sugita, Yuichi v Clezar, Guilherme [244] | 6-2,7-5,7-6 | |
| Challenger Quito | 09/01 16:30 | 27 | [133] Nicolas Jarry v Clezar, Guilherme [223] | 4-6,7-6,6-4 | |
| Challenger Quito | 08/30 17:15 | 26 | [271] Quiroz, Roberto v Clezar, Guilherme [223] | 3-6,7-6,2-6 | |
| Challenger Quito | 08/29 17:30 | 25 | Salamanca Caicedo, Carlos v Clezar, Guilherme | Retired | |
| Santo Domingo, Dominican Republic | 08/16 02:20 | 25 | [73] Damir Dzumhur v Clezar, Guilherme [219] | 7-6,6-3 | |
| Floridablanca, Colombia | 08/10 20:55 | 27 | Clezar, Guilherme v Gonzalo Lama | 6-2,4-6,4-6 | |
| Floridablanca, Colombia | 08/09 16:00 | 26 | [219] Clezar, Guilherme v Sorgi, Joao Pedro [284] | 6-3,6-4 | |
| Floridablanca, Colombia | 08/08 16:00 | 25 | [219] Clezar, Guilherme v Benjamin Lock [453] | 6-3,6-3 | |
| Challenger Liberec | 08/06 10:00 | 29 | [143] Sousa, Pedro v Clezar, Guilherme [264] | 6-4,5-7,6-2 | |
| Challenger Liberec | 08/05 09:30 | 28 | [204] Safranek, Vaclav v Clezar, Guilherme [264] | 6-1,2-6,3-6 | |
| Challenger Liberec | 08/04 10:00 | 27 | [264] Clezar, Guilherme v Oscar Otte [148] | 6-1,6-1 | |
| Challenger Liberec | 08/02 14:30 | 26 | [173] Lukas Rosol v Clezar, Guilherme [264] | 6-7,3-6 | |
| Challenger Liberec | 07/31 09:00 | 25 | [255] Tristan Lamasine v Clezar, Guilherme [264] | 6-1,1-6,4-6 | |
| Challenger Cortina | 07/26 09:25 | 26 | [166] Gerald Melzer v Clezar, Guilherme [272] | 7-6,6-3 | |
| Challenger Cortina | 07/24 10:00 | 25 | [297] Donati, Matteo v Clezar, Guilherme [272] | 6-7,6-2,5-7 | |
| Poznan, Poland | 07/18 09:00 | 25 | [188] Satral, Jan v Clezar, Guilherme [270] | 7-6,6-0 | |
| Milan, Italy | 06/29 16:35 | 26 | [206] Robredo, Tommy v Clezar, Guilherme [276] | 6-7,7-6,6-3 | |
| Milan, Italy | 06/26 13:20 | 25 | [276] Clezar, Guilherme v Thiago Monteiro [98] | 6-3,6-3 | |
| Challenger Todi | 06/20 09:30 | 25 | [273] Clezar, Guilherme v Gastao Elias [110] | 6-3,3-6,4-6 | |
| Lisbon, Portugal | 06/13 16:30 | 25 | [378] Frederico Ferreira Silva v Clezar, Guilherme [269] | 6-2,6-4 | |
| ITF Spain F16 | 06/07 10:15 | 26 | Vega Hernandez, David v Clezar, Guilherme | 6-4,6-4 | |
| ITF Spain F16 | 06/06 09:00 | 25 | [400] Ouahab, Lamine v Clezar, Guilherme [267] | 7-6,1-6,4-6 | |
| ITF Italy F15 | 05/30 13:30 | 25 | [353] Mina, Gianni v Clezar, Guilherme [267] | 4-6,6-1,6-2 | |
| Challenger - Francavilla | 04/25 14:55 | 25 | [278] Clezar, Guilherme v Matteo Berrettini [269] | 7-6,1-6,3-6 | |
| ITF Italy F9 | 04/22 09:30 | 29 | [277] Clezar, Guilherme v Salvatore Caruso [218] | 3-6,3-6 | |
| ITF Italy F9 | 04/21 10:30 | 28 | [255] Maden, Yannick v Clezar, Guilherme [277] | 5-7,4-6 | |
| ITF Italy F9 | 04/20 12:30 | 27 | [277] Clezar, Guilherme v Stefanos Tsitsipas [201] | 6-4,7-6 | |
| ITF Italy F9 | 04/19 14:50 | 26 | [277] Clezar, Guilherme v Baldi, Filippo [446] | 6-2,6-3 | |
| ITF Italy F9 | 04/17 16:55 | 25 | [277] Clezar, Guilherme v Williams, Rhyne [303] | 7-6,7-5 | |
| Challenger Barletta Qual | 04/10 08:00 | 54 | [238] Clezar, Guilherme v Lorenzo Sonego [311] | 5-7,4-6 |