Ground: Clay
| ITF Turkey F34 | 2014/09/28 07:00 | Nagao, Katsuki v Watanuki, Keisuke | 6-3,5-7,7-6 |
| ITF Japan F8 | 2015/06/25 04:25 | Ehara, Hiroyasu v Nagao, Katsuki | 4-6,3-6 |
| ITF Japan F8 | 2015/06/24 01:10 | Nagao, Katsuki v Osafune, Masaki | 6-3,6-0 |
| ITF Japan F7 | 2015/06/18 02:00 | Tanuma, Ryota v Nagao, Katsuki | 6-3,6-1 |
| ITF Japan F7 | 2015/06/17 01:00 | Takeshima, Shunrou v Nagao, Katsuki | 6-7,3-6 |
| ITF Japan F6 | 2015/06/10 01:30 | Yosuke Watanuki v Nagao, Katsuki | 7-6,6-7,6-4 |
| ITF Japan F5 | 2015/06/02 01:00 | Mclachlan, Ben v Nagao, Katsuki | 6-1,6-2 |
| ITF Guam F1 | 2015/05/30 02:20 | Suzuki, Takao v Nagao, Katsuki | 2-6,6-4,6-2 |
| ITF Guam F1 | 2015/05/29 01:40 | Nagao, Katsuki v Moore, B. | 2-6,6-4,6-2 |
| ITF Japan F8 | 2015/06/25 01:00 | Numajiri, Keisuke v Watanuki, Keisuke | 3-6,3-6 |
| ITF Japan F8 | 2015/06/24 02:45 | Watanuki, Keisuke v Ito, Yuichi | 6-1,7-5 |
| ITF Japan F7 | 2015/06/16 02:15 | Onozawa, Arata v Watanuki, Keisuke | 7-6,0-6,6-3 |
| ITF Japan F6 | 2015/06/11 02:55 | Niki, Takuto v Watanuki, Keisuke | 6-7,7-6,6-4 |
| ITF Japan F6 | 2015/06/10 01:30 | Watanuki, Keisuke v Oku, Hiromasa | 6-2,6-3 |
| ITF Japan F5 | 2015/06/04 02:00 | Thomas Fancutt v Watanuki, Keisuke | 7-5,7-6 |
| ITF Japan F5 | 2015/06/03 06:30 | Ryotaro Matsumura v Watanuki, Keisuke | 6-2,4-6,0-6 |
| ITF Greece F9 | 2015/04/29 10:05 | Simunek, David v Watanuki, Keisuke | 6-4,6-2 |