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