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.

Seeds

• # Roger Federer (semifinals) • # 🇪🇸 Rafael Nadal (round robin) • # 🇷🇸 Novak Djokovic (round robin) • # 🇬🇧 Andy Murray (round robin) • # 🇦🇷 Juan Martín del Potro (final) • # 🇷🇺 Nikolay Davydenko (champion) • # 🇪🇸 Fernando Verdasco (round robin) • # 🇸🇪 Robin Söderling (semifinals)

Alternates

• # 🇫🇷 Jo-Wilfried Tsonga (Did not play) • # Ivan Ljubičić (Did not play)

Draw

Finals

Group A

''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.''

Group B

''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.''