Alec Deckers defeated Guy Den Heijer 6-4 7-6 in the M15 Heraklion 6 round of 16 on hard. The upset overturned the form book — Guy Den Heijer came in leading the head-to-head 1–0. Alec Deckers claimed a first win over Guy Den Heijer in two meetings, narrowing the head-to-head to 1–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2021-06-21 | M25 Alkmaar 1 | Q32 | clay | Guy Den Heijer | 6-3 6-7(5) 10-4 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.