| Challenger Sarasota | 04/19 15:40 | 26 | [241] Guilherme Clezar v Evan King [192] | 7-6,3-6,6-2 | |
| Challenger Sarasota | 04/17 14:00 | 25 | [113] Taro Daniel v Guilherme Clezar [241] | 6-3,2-6,4-6 | |
| Challenger Città del Messico | 04/10 17:00 | 25 | [308] Joao Souza v Guilherme Clezar [233] | 7-6,7-5 | |
| Coppa Davis | 04/08 01:40 | 28 | Santiago Giraldo v Guilherme Clezar | Cancelled | |
| Coppa Davis | 04/06 21:20 | 28 | [257] Daniel Elahi Galan v Guilherme Clezar [234] | 3-6,6-2,6-1 | |
| Challenger Santiago | 03/05 18:55 | 25 | Guilherme Clezar v Thomaz Bellucci | View | |
| ATP San Paolo | 03/01 18:05 | 26 | Albert Ramos-Vinolas v Guilherme Clezar | 6-3,6-4 | |
| ATP San Paolo | 02/28 02:05 | 25 | Guilherme Clezar v Thiago Monteiro | 6-3,1-6,7-5 | |
| ATP San Paolo - Qual. | 02/25 16:10 | - | Pedro Sakamoto v Guilherme Clezar | 2-6,1-6 | |
| ATP San Paolo - Qual. | 02/24 19:20 | 26 | Fernando Yamacita v Guilherme Clezar | 1-6,6-7 | |
| ATP Rio de Janeiro - Qual. | 02/17 18:00 | 26 | Guilherme Clezar v Alessandro Giannessi | 7-6,4-6,3-6 | |
| ATP Buenos Aires - Qual. | 02/11 16:00 | - | Rogerio Dutra Silva v Guilherme Clezar | 7-6,7-6 | |
| ATP Buenos Aires - Qual. | 02/10 14:00 | 26 | Guilherme Clezar v Renzo Olivo | 7-5,6-0 | |
| ATP Quito - Qual. | 02/03 16:00 | 26 | Gonzalo Escobar v Guilherme Clezar | 6-7,7-6,6-4 | |
| Challenger Newport Beach | 01/22 19:55 | 25 | Guilherme Clezar v Stefan Kozlov | 2-6,3-6 | |
| Challenger - Rio De Janeiro | 11/24 19:00 | 27 | [125] Carlos Berlocq v Guilherme Clezar [222] | 7-5,6-1 | |
| Challenger - Rio De Janeiro | 11/23 14:00 | 26 | [338] Christian Lindell v Guilherme Clezar [222] | 3-6,0-6 | |
| Challenger - Rio De Janeiro | 11/21 18:00 | 25 | [222] Guilherme Clezar v Goncalo Oliveira [212] | 3-6,6-3,6-3 | |
| Challenger Santiago 2 | 11/14 22:00 | 25 | [222] Guilherme Clezar v Gonzalo Lama [452] | 4-6,6-2,3-6 | |
| Challenger Montevideo | 11/08 17:00 | 26 | [97] Nicolas Kicker v Guilherme Clezar [228] | 6-3,6-1 | |
| Challenger Montevideo | 11/06 21:55 | 25 | [166] Attila Balazs v Guilherme Clezar [228] | 6-7,6-7 | |
| Challenger Lima | 10/24 15:30 | 25 | [225] Blaz Rola v Guilherme Clezar [200] | 7-6,6-0 | |
| Challenger Cali 2 | 10/21 16:00 | 29 | [232] Guilherme Clezar v Federico Delbonis [69] | 6-7,5-7 | |
| Challenger Cali 2 | 10/20 20:30 | 28 | [184] Andrej Martin v Guilherme Clezar [232] | 6-7,3-6 | |
| Challenger Cali 2 | 10/20 00:00 | 27 | [232] Guilherme Clezar v Alejandro Gonzalez [436] | 6-4,6-1 | |
| Challenger Cali 2 | 10/18 18:05 | 26 | [232] Guilherme Clezar v Christian Garin [197] | 7-5,7-6 | |
| Challenger Cali 2 | 10/16 19:10 | 25 | Victor Estrella Burgos v Guilherme Clezar | 5-7,5-7 | |
| Challenger Buenos Aires | 10/10 14:00 | 25 | Guilherme Clezar v Michael Linzer | 3-6,7-6,3-6 | |
| Challenger Campinas | 10/05 16:40 | 26 | [146] Gastao Elias v Guilherme Clezar [238] | 6-4,7-6 | |
| Challenger Campinas | 10/03 19:00 | 25 | [238] Guilherme Clezar v Christian Lindell [334] | 6-3,6-2 |