| POS | Rank | Heat | BIB | ATHLETE | COUNTRY | RESULTS | ms* |
|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 147 | Jonathan SACOOR |
BEL |
45.72 Q NU20R | |
| 2 | 1 | 2 | 402 | Edoardo SCOTTI |
ITA |
45.84 Q NU20R | |
| 3 | 1 | 3 | 417 | Christopher TAYLOR |
JAM |
46.18 Q | |
| 4 | 2 | 1 | 419 | Chantz Sawyers |
JAM |
46.19 Q | |
| 5 | 2 | 2 | 145 | Jonathan JONES |
BAR |
46.22 Q | |
| 6 | 2 | 3 | 181 | Khamal Stewart-Baynes |
CAN |
46.38 Q | |
| 7 | 3 | 3 | 642 | Howard Fields |
USA |
46.53 q | .524 |
| 8 | 3 | 2 | 186 | Myles MISENER-DALEY |
CAN |
46.53 q | .526 |
| 9 | 3 | 1 | 207 | Matěj KRSEK |
CZE |
46.59 NU20R | |
| 10 | 4 | 2 | 662 | Umajesty Williams |
USA |
46.72 | |
| 11 | 4 | 1 | 174 | Bruno Silva |
BRA |
46.74 | .736 |
| 12 | 4 | 3 | 519 | Szymon Kreft |
POL |
46.74 | .740 |
| 13 | 5 | 3 | 565 | Aruna DHARSHANA |
SRI |
46.75 | |
| 14 | 5 | 2 | 233 | Alfredo Jimenez |
ESP |
46.93 PB | |
| 15 | 6 | 3 | 177 | Musa ISAH |
BRN |
46.94 | |
| 16 | 5 | 1 | 397 | Klaudio Gjetja |
ITA |
47.10 | |
| 17 | 6 | 2 | 669 | Kennedy LUCHEMBE |
ZAM |
47.35 | |
| 18 | 6 | 1 | 578 | Ricky PETRUCCIANI |
SUI |
47.39 | |
| 19 | 7 | 2 | 551 | Gabriel Louw |
RSA |
47.63 | |
| 20 | 7 | 3 | 316 | Jean Paul BREDAU |
GER |
47.70 | |
| 21 | 7 | 1 | 115 | Christian Davis |
AUS |
47.86 | |
| 22 | 8 | 2 | 564 | Boško KIJANOVIĆ |
SRB |
48.15 | |
| 23 | 8 | 1 | 511 | Antonio Grant |
PAN |
48.23 | |
| 3 | 468 | Ilhwan Mo |
KOR |
DQ |
ms - Milliseconds - shown when two or more competitors finish with the same time down to hundredths of a second