| Champ: |  Kei Nishikori |
| Score: | 4–6, 6–4, 6–4 |
| Draw: | 48 (6 / 4) |
| Seeds: | 16 |
| Main Name: | Washington Open (tennis) Washington Open |
See main article: 2015 Citi Open.
Milos Raonic was the defending champion, but chose not to participate this year.
Kei Nishikori won the title, defeating John Isner in the final, 4–6, 6–4, 6–4.
All seeds receive a bye into the second round.