Ryo Oki defeated Tetsuya Chaen 2-6 6-4 6-4 in the Japan F3 round of 32 on carpet. The upset overturned the form book — Tetsuya Chaen came in leading the head-to-head 1–0. Ryo Oki claimed a first win over Tetsuya Chaen in two meetings, narrowing the head-to-head to 1–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 1998-10-07 | Japan F4 | R16 | carpet | Tetsuya Chaen | 3-6 6-4 6-1 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.