2013 U.S. National Indoor Tennis Championships – Men's singles

Jürgen Melzer was the defending champion, but lost in the first round to Igor Sijsling. Kei Nishikori won the title, defeating Feliciano López in the final, 6–2, 6–3.

Seeds
• # Marin Čilić (quarterfinals)

• # 🇨🇦 Milos Raonic (first round)

• # 🇺🇸 John Isner (first round)

• # 🇺🇸 Sam Querrey (second round)

• # 🇯🇵 Kei Nishikori (champion)

• # 🇩🇪 Tommy Haas (second round, withdrew because of a viral illness)

• # 🇺🇦 Alexandr Dolgopolov (quarterfinals)

• # 🇪🇸 Fernando Verdasco (withdrew because of a neck injury)

Seeds
• # 🇺🇸 Michael Russell (qualifying competition, lucky loser)

• # 🇺🇸 Tim Smyczek (first round)

• # 🇩🇪 Philipp Petzschner (first round)

• # 🇦🇺 Matthew Ebden (qualifying competition)

• # 🇷🇺 Alex Bogomolov Jr. (qualified)

• # 🇨🇦 Vasek Pospisil (first round)

• # 🇺🇦 Illya Marchenko (qualified)

• # 🇺🇸 Denis Kudla (first round)

Qualifiers
• # 🇺🇸 Donald Young

• # 🇺🇸 Rhyne Williams

• # 🇷🇺 Alex Bogomolov Jr.

• # 🇺🇦 Illya Marchenko

Lucky losers

 * 1) 🇺🇸 Michael Russell