| Men's singles | |
|---|---|
| 2023 Keio Challenger | |
| Champion |  Yosuke Watanuki |
| Runner-up | Yuta Shimizu |
| Score | 7–6(7–5), 6–4 |
Christopher O'Connell was the defending champion [1] but chose not to defend his title.
Yosuke Watanuki won the title after defeating Yuta Shimizu 7–6(7–5), 6–4 in the final.
Yosuke Watanuki (champion)
Jurij Rodionov (first round)
Michael Mmoh (semifinals)
James Duckworth (second round, withdrew) Maxime Cressy (withdrew)
Luca Nardi (quarterfinals) Marc Polmans (second round)
Leandro Riedi (second round)| Semifinals | Final | ||||||||||||
| 1 | Yosuke Watanuki | 6 | 62 | 6 | |||||||||
| 3 | Michael Mmoh | 4 | 77 | 0 | |||||||||
| 1 | Yosuke Watanuki | 77 | 6 | ||||||||||
| Yuta Shimizu | 65 | 4 | |||||||||||
| Yuta Shimizu | w/o | ||||||||||||
| Q | Yasutaka Uchiyama | ||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 1 | Y Watanuki | 6 | 6 | ||||||||||||||||||||||||
 Y-h Hsu | 3 | 3 | 1 | Y Watanuki | 6 | 6 | |||||||||||||||||||||
| Q |  C Sinclair | 3 | 2 | LL |  M Erhard | 4 | 3 | ||||||||||||||||||||
| LL | Mathys Erhard | 6 | 6 | 1 | Y Watanuki | 3 | 6 | 6 | |||||||||||||||||||
| Q |  A Holmgren | 4 | 1 | LL | G Fonio | 6 | 2 | 1 | |||||||||||||||||||
| LL | G Fonio | 6 | 6 | LL | G Fonio | 4 | 77 | 6 | |||||||||||||||||||
| WC | R Noguchi | 2 | 2 | 8 | L Riedi | 6 | 64 | 4 | |||||||||||||||||||
| 8 | L Riedi | 6 | 6 | 1 | Y Watanuki | 6 | 62 | 6 | |||||||||||||||||||
| 3 | M Mmoh | 6 | 6 | 3 | M Mmoh | 4 | 77 | 0 | |||||||||||||||||||
 M Echargui | 1 | 2 | 3 | M Mmoh | 6 | 5 | 77 | ||||||||||||||||||||
| G Blancaneaux | 6 | 61 | 6 | G Blancaneaux | 4 | 7 | 63 | ||||||||||||||||||||
| Q | O Jasika | 4 | 77 | 3 | 3 | M Mmoh | 78 | 2 | 6 | ||||||||||||||||||
| Q |  K Ivanovski | 6 | 5 | 6 | 6 | L Nardi | 66 | 6 | 4 | ||||||||||||||||||
 Z Bergs | 1 | 7 | 2 | Q | K Ivanovski | 2 | 4 | ||||||||||||||||||||
| LL |  Y-s Chung | 2 | 4 | 6 | L Nardi | 6 | 6 | ||||||||||||||||||||
| 6 | L Nardi | 6 | 6 | ||||||||||||||||||||||||
| First round | Second round | Quarterfinals | Semifinals | ||||||||||||||||||||||||
| 7 | M Polmans | 6 | 6 | ||||||||||||||||||||||||
 C İlkel | 1 | 0 | 7 | M Polmans | 4 | 4 | |||||||||||||||||||||
| J Jung | 4 | 5 | Y Shimizu | 6 | 6 | ||||||||||||||||||||||
| Y Shimizu | 6 | 7 | Y Shimizu | 79 | 61 | 77 | |||||||||||||||||||||
| Alt | A Çelikbilek | 6 | 3 | 2 |  C Wong | 67 | 77 | 64 | |||||||||||||||||||
| C Wong | 2 | 6 | 6 | C Wong | w/o | ||||||||||||||||||||||
 Z Kolář | 2 | 77 | 2 | 4 | J Duckworth | ||||||||||||||||||||||
| 4 | J Duckworth | 6 | 64 | 6 | Y Shimizu | w/o | |||||||||||||||||||||
| Q | N Nakagawa | 65 | 6 | 2 | Q | Y Uchiyama | |||||||||||||||||||||
| A Martin | 77 | 1 | 6 | A Martin | 6 | 4 | 5 | ||||||||||||||||||||
| WC | Rei Sakamoto | 4 | 3 | L Tu | 2 | 6 | 7 | ||||||||||||||||||||
| L Tu | 6 | 6 | L Tu | 61 | 5 | ||||||||||||||||||||||
| Q | Y Uchiyama | 6 | 6 | Q | Y Uchiyama | 77 | 7 | ||||||||||||||||||||
| WC | M Imamura | 1 | 1 | Q | Y Uchiyama | 2 | 6 | 6 | |||||||||||||||||||
| S-c Hong | 78 | 78 | S-c Hong | 6 | 4 | 4 | |||||||||||||||||||||
| 2 | J Rodionov | 66 | 66 | ||||||||||||||||||||||||
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.
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.
James Duckworth was the defending champion but chose not to defend his title.
Maxime Cressy was the defending champion but lost in the third round to Ulises Blanch.
Ričardas Berankis 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.
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.
Frances Tiafoe defeated Tomás Martín Etcheverry in the final, 7–6(7–1), 7–6(8–6) to win the singles tennis title at the 2023 U.S. Men's Clay Court Championships. It was Tiafoe's first ATP Tour title in five years.
Yasutaka Uchiyama was the defending champion but retired from his second round match against Christopher O'Connell.
Yosuke Watanuki was the defending champion but chose not to defend his title.