2004 AIG Japan Open Tennis Championships – Men's singles

Rainer Schüttler was the defending champion, but did not participate.

Seeds
All seeds receive a bye into the second round. • # 🇦🇺 Lleyton Hewitt (semifinals)

• # 🇦🇷 David Nalbandian (third round)

• # 🇷🇴 Andrei Pavel (second round)

• # 🇹🇭 Paradorn Srichaphan (quarterfinals)

• # 🇨🇿 Jiří Novák (champion)

• # 🇦🇷 Guillermo Cañas (second round)

• # 🇺🇸 Taylor Dent (final)

• # 🇸🇪 Thomas Johansson (third round)

• # 🇫🇷 Cyril Saulnier (quarterfinals)

• # 🇰🇷 Hyung-Taik Lee (third round)

• # 🇧🇷 Ricardo Mello (third round)

• # 🇫🇮 Jarkko Nieminen (second round)

• # 🇺🇸 Jan-Michael Gambill (third round)

• # Dennis van Scheppingen (second round)

• # 🇨🇿 Jan Hernych (second round)

• # 🇱🇺 Gilles Müller (quarterfinals)