Tetsuya Chaen defeated Ryo Oki 3-6 6-4 6-1 in the Japan F4 round of 16 on carpet. The upset overturned the form book — Ryo Oki came in leading the head-to-head 1–0. Tetsuya Chaen claimed a first win over Ryo Oki in two meetings, narrowing the head-to-head to 1–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 1998-09-30 | Japan F3 | R32 | carpet | Ryo Oki | 2-6 6-4 6-4 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.