Ruben Alvarenga defeated Joao Zwetsch 5-7 6-4 6-4 in the Uruguay Paraguay Masters 4 round of 16 on clay. The upset overturned the form book — Joao Zwetsch came in leading the head-to-head 2–0. Ruben Alvarenga claimed a first win over Joao Zwetsch in three meetings, narrowing the head-to-head to 2–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 1991-04-15 | Brazil 2 Masters 3 | R16 | clay | Joao Zwetsch | 6-2 7-6 |
| 1991-04-15 | Brazil 2 Masters 4 | QF | clay | Joao Zwetsch | 6-0 6-4 |