| ITF M25 Tainan | 08/15 02:00 | 25 | Seita Watanabe v Takuya Kumasaka | 3-6,6-4,2-6 | |
| ITF M25 Astana | 08/03 10:50 | 26 | [446] Khumoyun Sultanov v Seita Watanabe [298] | 4-6,6-3,7-5 | |
| ITF M25 Astana | 08/02 10:25 | 25 | Seita Watanabe v Timur Maulenov | 3-6,6-3,6-2 | |
| ITF M25 Astana | 08/01 05:20 | 54 | Seita Watanabe v Mykhailo Mossur | 6-4,6-3 | |
| ITF M25 Astana | 07/31 05:40 | 54 | Seita Watanabe v Vitaliy Zatsepin | 6-2,6-2 | |
| Challenger Astana | 07/23 10:35 | 14 | [287] Seita Watanabe v Egor Agafonov [432] | 2-6,2-6 | |
| ITF M15 Monastir | 07/19 14:20 | 25 | Seita Watanabe v Gilbert Klier Junior | 2-6,6-2,2-6 | |
| ITF M15 Monastir | 07/17 15:00 | 62 | Seita Watanabe v Vyacheslav Ovchinnikov | 6-2,6-2 | |
| ITF M15 Monastir | 07/16 08:00 | 62 | Seita Watanabe v Alberto Bronzetti | 6-2,6-3 | |
| ITF M15 Monastir | 07/12 09:25 | 25 | Seita Watanabe v Cyril Vandermeersch | 5-7,3-6 | |
| ITF M25 Santo Domingo | 06/27 15:30 | 25 | [351] Bernard Tomic v Seita Watanabe [326] | 6-4,6-3 | |
| ITF M15 Santo Domingo | 06/21 13:30 | 25 | Tauheed Browning v Selta Watanabe | 7-6,0-6,7-5 | |
| ITF M15 Karuizawa | 05/31 01:00 | 25 | Jumpei Yamasaki v Seita Watanabe | 6-4,6-4 | |
| UTR Pro Miki | 02/12 02:00 | - | Tomohiro Masabayashi v Seita Watanabe | 4-6,1-5 | |
| UTR Pro Miki | 02/11 03:30 | - | Yuichiro Inui v Seita Watanabe | 6-7,6-7 | |
| UTR Pro Miki | 02/10 04:30 | - | Ren Nakamura v Seita Watanabe | 5-7,2-6 | |
| UTR Pro Miki | 02/09 03:30 | - | Kosuke Shibano v Seita Watanabe | 2-6,1-6 | |
| UTR Pro Miki | 02/08 03:30 | - | Ryohei Takase v Seita Watanabe | 2-6,1-5 | |
| UTR Pro Miki | 02/06 03:30 | - | Ryotaro Taguchi v Seita Watanabe | 6-2,6-7,7-6 | |
| Challenger Kobe | 11/13 01:00 | 14 | [349] Mukund Sasikumar v Seita Watanabe [383] | 6-3,6-1 | |
| ITF M25 Jakarta | 10/27 02:00 | 26 | [434] Thomas Fancutt v Seita Watanabe [422] | 7-5,7-5 | |
| ITF M25 Jakarta | 10/26 04:20 | 25 | Congsup Congcar v Seita Watanabe | 2-6,2-6 | |
| Challenger Busan | 10/16 01:30 | 14 | [287] Max Purcell v Seita Watanabe [373] | 6-0,6-2 | |
| Challenger Seoul | 10/09 05:25 | 14 | [253] Hiroki Moriya v Seita Watanabe [401] | 6-3,6-2 | |
| Challenger Gwangju | 10/03 04:00 | 19 | [397] Yunseong Chung v Seita Watanabe [401] | 6-2,7-6 | |
| Challenger Gwangju | 10/02 06:00 | 14 | Woohyuk Sim v Seita Watanabe | 2-6,0-6 | |
| ITF M25 Kashiwa | 09/29 01:00 | 26 | [290] Rio Noguchi v Seita Watanabe [402] | 6-7,6-3,6-3 | |
| ITF M25 Kashiwa | 09/28 02:20 | 25 | Yudai Umeoka v Seita Watanabe | 1-6,1-6 | |
| Challenger Nonthaburi - Kval | 09/04 08:30 | 14 | [432] Seita Watanabe v Timo Legout [495] | 2-6,6-4,2-6 | |
| ITF M15 Cancun | 08/16 14:00 | 25 | Kalman L. Boyd v Seita Watanabe | 6-2,6-4 |