Athletics at the 2008 Summer Olympics – Men's 400 metres Semifinal 1 Semifinal 1

| Rank_ | Lane | Athlete | Nationality | Time_ | React |
|---|---|---|---|---|---|
| 1 | 6 | Jeremy Wariner | United States | 44.15 | 0.224 |
| 2 | 5 | Chris Brown | Bahamas | 44.59 | 0.244 |
| 3 | 6 | Kévin Borlée | Belgium | 44.88 | 0.162 |
| 4 | 7 | Nery Brenes | Costa Rica | 44.94 | 0.169 |
| 5 | 4 | Saul Weigopwa | Nigeria | 45.02 | 0.168 |
| 6 | 2 | William Collazo | Cuba | 45.06 | 0.191 |
| 7 | 8 | Tabarie Henry | Virgin Islands | 45.19 | 0.165 |
| 8 | 2 | Claudio Licciardello | Italy | 45.64 | 0.259 |