Mathias Huning defeated Carlos Zwetsch 6-1 7-5 in the Brazil 1 Masters 1 round of 32 on clay. The upset overturned the form book — Carlos Zwetsch came in leading the head-to-head 1–0. Mathias Huning claimed a first win over Carlos Zwetsch in two meetings, narrowing the head-to-head to 1–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 1991-04-15 | Brazil 2 Masters 3 | R16 | clay | Carlos Zwetsch | 6-2 7-6 |