| Men's singles | |
|---|---|
| 2024 Keio Challenger | |
| 2023 Champion |  Yosuke Watanuki |
Yosuke Watanuki was the defending champion [1] but chose not to defend his title.
| Men's singles | |
|---|---|
| 2024 Keio Challenger | |
| 2023 Champion | Yosuke Watanuki |
Yosuke Watanuki was the defending champion [1] but chose not to defend his title.
| Semifinals | Final | ||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 |  M Bellucci | ||||||||||||||||||||||||||
 T-l Wu | |||||||||||||||||||||||||||
 Alexey Zakharov | |||||||||||||||||||||||||||
| R Noguchi | |||||||||||||||||||||||||||
 M Dodig | |||||||||||||||||||||||||||
 N Basilashvili | |||||||||||||||||||||||||||
| Q | |||||||||||||||||||||||||||
| 8 |  C Lestienne | ||||||||||||||||||||||||||
| 3 |  C Wong | ||||||||||||||||||||||||||
| WC | Lennon Roark Jones | ||||||||||||||||||||||||||
| Q | |||||||||||||||||||||||||||
| S Mochizuki | |||||||||||||||||||||||||||
 A Blockx | |||||||||||||||||||||||||||
| Q | |||||||||||||||||||||||||||
| Y Demin | |||||||||||||||||||||||||||
| 6 |  L Tu | ||||||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 7 |  J Rodionov | ||||||||||||||||||||||||||
| WC | R Sakamoto | ||||||||||||||||||||||||||
| Q | |||||||||||||||||||||||||||
 G den Ouden | |||||||||||||||||||||||||||
| WC | M Imamura | ||||||||||||||||||||||||||
| D Sweeny | |||||||||||||||||||||||||||
| Y Shimizu | |||||||||||||||||||||||||||
| 4 | A Bolt | ||||||||||||||||||||||||||
| 5 | S Shimabukuro | ||||||||||||||||||||||||||
 B Hassan | |||||||||||||||||||||||||||
 D Svrčina | |||||||||||||||||||||||||||
| Q | |||||||||||||||||||||||||||
| Q | |||||||||||||||||||||||||||
| J McCabe | |||||||||||||||||||||||||||
 E Ymer | |||||||||||||||||||||||||||
| 2 | Y Uchiyama | ||||||||||||||||||||||||||
Félix Auger-Aliassime and Denis Shapovalov were the defending champions, however Shapovalov withdrew due to injury. Auger-Aliassime played alongside Benjamin Sigouin, but lost in the final to Juan Carlos Aguilar and Felipe Meligeni Alves, 3–6, 6–7(4–7).
Ilya Ivashka was the defending champion but chose not to defend his title.
Alexander Zverev was the defending champion and successfully defended his title, defeating Alex de Minaur in the final, 6–2, 6–4.
David Goffin was the defending champion, but withdrew before the competition began.
Matthew Ebden was the defending champion but chose not to defend his title.
Stéphane Robert was the defending champion but chose not to defend his title.
Frances Tiafoe was the defending champion, but lost in the first round to Dan Evans.
Peter Polansky was the defending champion but lost in the semifinals to Yasutaka Uchiyama.
Lloyd Harris was the defending champion but chose not to defend his title.
Rogério Dutra Silva was the defending champion but chose not to defend his title.
Cameron Norrie defeated Alex Molčan in the final, 6–3, 6–7(3–7), 6–1 to win the singles tennis title at the 2022 ATP Lyon Open. Norrie became the first Briton to win a clay court title on the ATP Tour since 2016.
Valentin Vacherot was the defending champion but lost in the quarterfinals to Beibit Zhukayev.
Arthur Cazaux was the defending champion but retired from his match with Stuart Parker in the final; 6–4, 4–1.
Yoshihito Nishioka defeated Denis Shapovalov in the final, 6–4, 7–6(7–5) to win the men's singles tennis title at the 2022 Korea Open. It was his first ATP Tour title since Shenzhen in 2018.
Kwon Soon-woo was the defending champion but chose not to defend his title.
Yosuke Watanuki was the defending champion and successfully defended his title, defeating Frederico Ferreira Silva 6–7(3–7), 7–5, 6–4 in the final.
Yūichi Sugita was the defending champion but lost in the second round to Colin Sinclair.
Yosuke Watanuki was the defending champion but chose not to defend his title.
Christopher O'Connell was the defending champion but chose not to defend his title.
Yosuke Watanuki was the defending champion but lost in the second round to Giovanni Fonio.