2018 Rakuten Japan Open Tennis Championships – Singles

David Goffin was the defending champion, but withdrew before the competition began.

Daniil Medvedev won the title, defeating Kei Nishikori in the final, 6–2, 6–4.

Seeds
• # Marin Čilić (first round)

• # Kevin Anderson (quarterfinals)

• #🇯🇵 Kei Nishikori (final)

• #🇦🇷 Diego Schwartzman (first round)

• # Stefanos Tsitsipas (quarterfinals)

• #🇨🇦 Milos Raonic (quarterfinals)

• #🇰🇷 Chung Hyeon (first round)

• #🇫🇷 Richard Gasquet (semifinals)

Seeds
• # 🇷🇺 Daniil Medvedev (qualified)

• # 🇸🇰 Martin Kližan (qualified)

• # 🇺🇸 Denis Kudla (qualified)

• # 🇺🇸 Mackenzie McDonald (first round)

• # 🇷🇴 Marius Copil (first round)

• # 🇺🇸 Bradley Klahn (qualifying competition)

• # 🇵🇱 Hubert Hurkacz (first round)

• # 🇺🇸 Tim Smyczek (first round)

Qualifiers
• # 🇷🇺 Daniil Medvedev

• # 🇸🇰 Martin Kližan

• # 🇺🇸 Denis Kudla

• # 🇯🇵 Yosuke Watanuki