Joost Winnink defeated Sander Groen 6-3 6-1 in the Rotterdam round of 32 on hard. The upset overturned the form book — Sander Groen came in leading the head-to-head 1–0. Joost Winnink claimed a first win over Sander Groen in two meetings, narrowing the head-to-head to 1–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 1991-06-24 | Netherlands Masters 1 | R16 | clay | Sander Groen | 2-6 6-2 6-1 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.