David Nalbandian defeated the two-time defending champion Roger Federer in the final, 6–7(4–7), 6–7(11–13), 6–2, 6–1, 7–6(7–3) to win the singles tennis title at the 2005 Tennis Masters Cup. Mariano Puerta's round-robin result was disqualified upon his doping charge in December 2005.

Seeds

• # Roger Federer (final) • # 🇪🇸 Rafael Nadal (withdrew due to a left foot injury) • # 🇺🇸 Andre Agassi (round robin, withdrew due to a left ankle sprain) • # 🇦🇷 Guillermo Coria (round robin) • # 🇷🇺 Nikolay Davydenko (semifinals) • # Ivan Ljubičić (round robin) • # 🇦🇷 Gastón Gaudio (semifinals) • # 🇦🇷 David Nalbandian (champion)

Alternates

• # 🇦🇷 Mariano Puerta (replaced Nadal, round robin) • # Fernando González (replaced Agassi, round robin) • # 🇸🇪 Thomas Johansson (Did not play)

Draw

Finals

Red group

''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.''

Gold group

''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.''