| Challenger de Samarcanda | 05/14 11:30 | 25 | [319] Aleksandar Vukic v Guilherme Clezar [273] | 7-5,6-4 | |
| Challenger de Aix-en-Provence | 05/06 10:00 | 24 | [263] Guilherme Clezar v Rogerio Dutra Silva [175] | 2-6,3-6 | |
| Challenger de Savannah | 04/30 19:55 | 25 | [354] Aleksandar Vukic v Guilherme Clezar [263] | 7-6,6-7,6-3 | |
| Challenger de Tallahassee | 04/24 14:00 | 25 | Guilherme Clezar v Sandro Ehrat | 7-6,5-7,2-6 | |
| Challenger de Sarasota | 04/18 18:50 | 26 | [244] Guilherme Clezar v Tennys Sandgren [111] | 6-7,2-6 | |
| Challenger de Sarasota | 04/17 14:00 | 25 | [183] Dominik Koepfer v Guilherme Clezar [244] | 7-6,3-6,5-7 | |
| Challenger de Sarasota | 04/16 14:00 | 24 | [374] Harri Heliovaara v Guilherme Clezar [244] | 2-6,4-6 | |
| Challenger de Zhangjiagang | 03/20 08:10 | 25 | [169] Soonwoo Kwon v Guilherme Clezar [256] | 7-6,6-3 | |
| Challenger de Zhangjiagang | 03/19 03:05 | 24 | [256] Guilherme Clezar v Harri Heliovaara [376] | 7-6,6-3 | |
| Challenger de Shenzhen | 03/12 02:00 | 24 | [259] Guilherme Clezar v Max Purcell [266] | 6-7,6-7 | |
| Challenger de Zhuhai | 03/07 08:20 | 26 | [259] Guilherme Clezar v Hiroki Moriya [174] | 3-6,4-6 | |
| Challenger de Zhuhai | 03/06 09:35 | 25 | [259] Guilherme Clezar v Runhao Hua [426] | 6-2,4-6,7-5 | |
| Challenger de Yokohama | 02/26 08:05 | 25 | [237] Guilherme Clezar v Gastao Elias [297] | 6-0,2-6,6-7 | |
| Challenger de Launceston | 01/29 02:00 | 25 | [234] Guilherme Clezar v Tsung-Hua Yang [283] | 5-7,6-7 | |
| Challenger de Burnie | 01/23 03:20 | 25 | [234] Guilherme Clezar v Jeremy Beale [298] | 2-6,4-6 | |
| Open de Australia | 01/08 03:30 | 44 | [235] Guilherme Clezar v Rudolf Molleker [207] | 6-7,6-7 | |
| Challenger de Nouméa | 12/31 01:50 | 24 | Marcelo Tomas Barrios Vera v Guilherme Clezar | 4-6,6-2,6-3 | |
| Challenger Buenos Aires | 11/16 18:10 | 27 | [254] Guilherme Clezar v Federico Coria [322] | 6-7,5-7 | |
| Challenger Buenos Aires | 11/15 17:00 | 26 | [276] Martin Cuevas v Guilherme Clezar [254] | 4-6,1-6 | |
| Challenger Buenos Aires | 11/12 16:05 | 25 | [270] Miljan Zekic v Guilherme Clezar [254] | 3-6,2-6 | |
| Challenger de Montevideo | 11/06 19:45 | 25 | [244] Guilherme Clezar v Pedro Sousa [114] | 1-6,2-6 | |
| Challenger de Guayaquil | 10/30 15:30 | 25 | [245] Facundo Arguello v Guilherme Clezar [240] | 4-6,6-2,6-1 | |
| Challenger de Lima | 10/24 16:00 | 26 | [246] Guilherme Clezar v Christian Garin [102] | 3-6,3-6 | |
| Challenger de Lima | 10/22 17:55 | 25 | Guilherme Clezar v Kento Tagashira | 6-0,6-0 | |
| Challenger de Campinas | 10/03 00:05 | 25 | [207] Guilherme Clezar v Christian Garin [141] | 7-6,6-7,4-6 | |
| US Open | 08/23 19:40 | 45 | [117] Lorenzo Sonego v Guilherme Clezar [204] | 7-5,5-7,6-3 | |
| US Open | 08/22 22:40 | 44 | [284] Ricardo Ojeda Lara v Guilherme Clezar [204] | 4-6,3-6 | |
| Challenger de Cordenons | 08/18 15:00 | 28 | [367] Mate Valkusz v Guilherme Clezar [236] | 6-2,6-4 | |
| Challenger de Cordenons | 08/17 12:30 | 27 | [236] Guilherme Clezar v Facundo Bagnis [153] | 6-4,4-6,6-2 | |
| Challenger de Cordenons | 08/15 13:10 | 26 | [236] Guilherme Clezar v Pedro Cachin [260] | 6-2,6-4 |