Ground: Hardcourt outdoor
| ITF M25 Sapporo | 2023/09/05 04:15 | Issei Okamura v Seiya Nakanishi | 6-1,6-1 |
| ITF M25 Tsukuba | 2023/03/27 00:30 | Seiya Nakanishi v Issei Okamura | 2-6,4-6 |
| ITF M15 Singapore | 2025/08/13 02:00 | Antoine Berger v Issei Okamura | 6-1,6-1 |
| ITF M15 Singapore | 2025/08/05 05:43 | Issei Okamura v Ammar Faleh Alhogbani | 2-6,6-4,3-6 |
| ITF M15 Bali | 2025/07/29 01:30 | Issei Okamura v Lucca Liu | 2-6,1-6 |
| ITF M15 Tokyo | 2025/07/01 01:00 | Issei Okamura v Yuta Tomida | 5-7,3-6 |
| ITF M15 Karuizawa | 2025/06/04 04:29 | Issei Okamura v Jay Friend | 3-6,2-6 |
| ITF M25 Anning | 2025/04/29 06:57 | Issei Okamura v Grigoriy Lomakin | 4-6,7-6,6-7 |
| ITF M15 Osaka | 2025/04/22 04:15 | Jumpei Yamasaki v Issei Okamura | 6-3,6-4 |
| ITF M15 Osaka | 2025/04/21 02:30 | Issei Okamura v Ryuichiro Nakano | 6-1,6-1 |
| ITF M15 Harmon | 2025/06/10 23:58 | Seiya Nakanishi v Kenta Miyoshi | 0-6,2-6 |
| UTR Pro Kawaguchi | 2025/04/27 05:05 | Seiya Nakanishi v Kenta Nakamura | 6-1,6-4 |
| UTR Pro Kawaguchi | 2025/04/27 01:00 | Seiya Nakanishi v Alexey Shtengelov | 6-7,6-4,7-5 |
| UTR Pro Kawaguchi | 2025/04/25 03:00 | Seiya Nakanishi v Masaki Tonaka | 6-7,6-3,7-5 |
| UTR Pro Kawaguchi | 2025/04/24 06:25 | Seiya Nakanishi v Ryota Tanuma | 3-6,4-6 |
| UTR Pro Kawaguchi | 2025/04/24 00:00 | Ko Nagashima v Seiya Nakanishi | 3-6,7-5,6-1 |
| UTR Pro Kawaguchi | 2025/04/22 02:10 | Hikaru Takahashi v Seiya Nakanishi | 4-6,7-5,6-1 |
| ITF M15 Osaka | 2025/04/15 01:00 | Yusuke Kusuhara v Seiya Nakanishi | 6-2,7-6 |