| Champ: |  Nikolay Davydenko |
| Runner: |  Juan Martín del Potro |
| Score: | 6–3, 6–4 |
| Type: | singles doubles |
| Before Name: | Tennis Masters Cup |
See main article: 2009 ATP World Tour Finals.
Nikolay Davydenko defeated Juan Martín del Potro in the final, 6–3, 6–4 to win the singles tennis title at the 2009 ATP World Tour Finals.
Novak Djokovic was the defending champion, but was eliminated in the round-robin stage.
Fernando Verdasco and Robin Söderling made their debuts at the event.
Andy Roddick qualified for the tournament, but withdrew due to a left leg injury, where he was replaced by Söderling.
Standings are determined by: 1. number of wins; 2. number of matches; 3. in two-players-ties, head-to-head records; 4. in three-players-ties, percentage of sets won, or of games won; 5. steering-committee decision.
Standings are determined by: 1. number of wins; 2. number of matches; 3. in two-players-ties, head-to-head records; 4. in three-players-ties, percentage of sets won, or of games won; 5. steering-committee decision.