Mariano Campos defeated Matias Oneille 7-5 6-2 in the Argentina 1 Masters 3 qualifying round on clay. The upset overturned the form book — Matias Oneille came in leading the head-to-head 1–0. Mariano Campos claimed a first win over Matias Oneille in two meetings, narrowing the head-to-head to 1–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2000-05-15 | Argentina F5 | R32 | clay | Matias Oneille | 6-1 6-4 |