| Champ: |  Donald McNeill[1] |
| Score: | 4–6, 6–8, 6–3, 6–3, 7–5 |
| Draw: | 78 |
| Seeds: | 10 |
Donald McNeill defeated Bobby Riggs 4–6, 6–8, 6–3, 6–3, 7–5 in the final to win the men's singles tennis title at the 1940 U.S. National Championships.[2]
The seeded players are listed below. Donald McNeill is the champion; others show the round in which they were eliminated.
Bobby Riggs (finalist) Donald McNeill (champion) Francis Kovacs (quarterfinals) Frank Parker (quarterfinals) Joseph Hunt (semifinals) Henry Prusoff (fourth round) Bryan Grant (fourth round) Elwood Cooke (quarterfinals) Gardnar Mulloy (first round) Welby Van Horn (second round)