Semifinal
samedi 15 décembre 2018, 12h15 GMT – 12h15 GMT
| Nom | Équipe | Temps | |
|---|---|---|---|
| 1 |  Chad Le Clos | South Africa | 45.89″ |
| 2 |  Vladimir Morozov | Russia | + 0.04″ |
| 3 |  Caeleb Dressel | United States | + 0.2″ |
| 4 | Vladislav Grinev | Russia | + 0.34″ |
| 5 |  Katsumi Nakamura | Japan | + 0.35″ |
| 6 | Blake Pieroni | United States | + 0.42″ |
| 7 |  Simonas Bilis | Lithuania | + 0.57″ |
| 8 |  Mehdy Metella | France | + 0.64″ |
| 9 |  Cameron McEvoy | Australia | + 0.8″ |
| 10 |  Alessandro Miressi | Italy | + 0.95″ |
| 11 | Sergiy Shevtsov | Ukraine | + 0.97″ |
| 12 |  Marcelo Chierighini | Brazil | + 1.04″ |
| 12 |  Shane Ryan | Ireland | + 1.04″ |
| 14 | Lorenzo Zazzeri | Italy | + 1.09″ |
| 15 |  Jesse Puts | Netherlands | + 1.34″ |
| 16 | Danas Rapšys | Lithuania | + 1.36″ |