| ITF M15 Hua Hin | 08/19 04:45 | 54 | Bang Shuo Yin v Seita Watanabe | 6-4,1-6,5-10 | |
| ITF M25 Taipei | 07/26 02:00 | 27 | Makoto Ochi v Seita Watanabe | 6-4,7-6 | |
| ITF M25 Taipei | 07/25 02:00 | 26 | Jonathan Mridha v Seita Watanabe | Retired | |
| ITF M25 Taipei | 07/24 02:00 | 25 | Seita Watanabe v Chien Hsun Lo | 6-2,6-2 | |
| ITF M25 Taipei | 07/23 02:00 | 54 | Taisei Ichikawa v Seita Watanabe | 5-7,4-6 | |
| ITF M25 Taipei | 07/17 02:00 | 25 | Yan Bai v Seita Watanabe | 6-0,6-2 | |
| ITF M25 Taipei | 07/16 03:50 | 54 | Ren Nakamura v Seita Watanabe | 6-4,4-6,5-10 | |
| ITF M25 Taipei | 07/15 04:30 | 54 | Mu Fu Tsai v Seita Watanabe | 0-6,0-6 | |
| ITF M15 Gimcheon | 06/18 03:20 | 54 | Seita Watanabe v Seong Taek Im | 3-6,7-6,12-14 | |
| ITF M15 Gimcheon | 06/17 01:00 | 54 | David Barclay v Seita Watanabe | Retired | |
| ITF M15 Gimcheon | 06/12 03:20 | 25 | Seong-Gook Oh v Seita Watanabe | 6-7,6-2,6-3 | |
| ITF M15 Gimcheon | 06/11 02:50 | 54 | Seita Watanabe v Hyung-Chan Lim | 6-4,6-0 | |
| ITF M15 Gimcheon | 06/10 02:00 | 54 | Seita Watanabe v Jin Sung Han | 6-1,6-2 | |
| ITF M15 Tegu | 06/06 02:00 | 26 | Jung-Woong Na v Seita Watanabe | 6-3,6-2 | |
| ITF M15 Tegu | 06/05 03:55 | 25 | Seita Watanabe v Issei Okamura | 6-4,7-6 | |
| ITF M15 Tegu | 06/04 02:20 | 54 | Seita Watanabe v Seunghun Shin | 6-0,6-1 | |
| ITF M15 Tegu | 06/03 05:00 | 54 | Seita Watanabe v Dae-Hee Lee | 6-2,6-0 | |
| ITF M15 Tabarka | 05/16 10:30 | 26 | Manuel Guinard v Seita Watanabe | 6-3,6-1 | |
| ITF M15 Tabarka | 05/15 08:00 | 25 | Seita Watanabe v Roman Blokhin | 6-1,6-0 | |
| ITF M15 Tabarka | 05/14 08:00 | 54 | Lluis Dolz v Seita Watanabe | 0-6,1-6 | |
| ITF M15 Tabarka | 05/07 10:35 | 25 | Anis Ghorbel v Seita Watanabe | 6-0,6-4 | |
| ITF M15 Tabarka | 05/01 08:30 | 25 | Seita Watanabe v Anas Fattar | 4-6,6-7 | |
| ITF M15 Tabarka | 04/29 13:30 | 54 | Gregorio Cordonnier v Seita Watanabe | 4-6,6-7 | |
| ITF M15 Tabarka | 04/29 08:00 | 54 | Pierre Gimla v Seita Watanabe | 0-6,0-6 | |
| ITF M15 Kashiwa | 04/01 00:00 | 45 | Ryota Tanuma v Seita Watanabe | 3-6,6-1,12-10 | |
| ITF M15 Kofu | 03/20 07:15 | 25 | Seita Watanabe v Sho Katayama | 3-6,2-6 | |
| ITF M15 Kofu | 03/18 06:30 | 45 | Keigo Shimizu v Seita Watanabe | 1-6,1-6 | |
| ITF M15 Kofu | 03/18 03:00 | 45 | Seita Watanabe v Shao-Fan Liu | 6-3,4-6,11-9 | |
| ITF - M15 Nishi-Tokyo | 03/12 05:00 | 25 | Makoto Ochi v Seita Watanabe | 6-1,6-2 | |
| Challenger Kobe | 11/11 06:10 | 46 | Blake Ellis v Seita Watanabe | 6-4,6-2 |