| POS | Rank | Heat | BIB | ATHLETE | COUNTRY | RESULTS | ms* |
|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | JAM | Jamaica U20 |
JAM |
43.28 Q | |
| 2 | 1 | 2 | USA | United States U20 |
USA |
43.66 Q SB | |
| 3 | 1 | 3 | GBR | Great Britain & NI U20 |
GBR |
43.78 Q NU20R | |
| 4 | 2 | 3 | COL | Colombia U20 |
COL |
44.34 Q NU20R | .332 |
| 5 | 3 | 3 | GER | Germany U20 |
GER |
44.34 q | .338 |
| 6 | 2 | 1 | ITA | Italy U20 |
ITA |
44.69 Q SB | |
| 7 | 2 | 2 | AUS | Australia U20 |
AUS |
44.83 Q SB | |
| 8 | 3 | 2 | SUI | Switzerland U20 |
SUI |
44.94 q SB | .940 |
| 8 | 4 | 3 | CZE | Czech Republic U20 |
CZE |
44.94 SB | .940 |
| 10 | 4 | 2 | POL | Poland U20 |
POL |
45.14 SB | |
| 11 | 3 | 1 | FRA | France U20 |
FRA |
45.20 SB | |
| 12 | 4 | 1 | RSA | South Africa U20 |
RSA |
45.84 SB | |
| 13 | 5 | 1 | PUR | Puerto Rico U20 |
PUR |
46.12 NU20R | |
| 14 | 6 | 1 | TTO | Trinidad and Tobago U20 |
TTO |
46.44 | |
| 15 | 7 | 1 | BAH | Bahamas U20 |
BAH |
46.51 SB | |
| 2 | FIN | Finland U20 |
FIN |
DQ | |||
| 3 | NGR | Nigeria U20 |
NGR |
DQ | |||
| 3 | BRA | Brazil U20 |
BRA |
DQ | |||
| 2 | CAN | Canada U20 |
CAN |
DNS |
ms - Milliseconds - shown when two or more competitors finish with the same time down to hundredths of a second