G. J. Kim defeated Colin Sinclair 7-6 6-3 in the M25 Harmon 2 round of 32 on hard. The upset overturned the form book — Colin Sinclair came in leading the head-to-head 2–0. G. J. Kim claimed a first win over Colin Sinclair in three meetings, narrowing the head-to-head to 2–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2025-06-12 | M15 Harmon 1 | R16 | hard | Colin Sinclair | 6-4 6-0 |
| 2022-08-17 | M15 Anseong 1 | R32 | clay | Colin Sinclair | 7-5 6-2 |