Chiaki Okadaue defeated Seiko Okamoto 6-3 6-2 in the Gunma 25K round of 16 on carpet. The upset overturned the form book — Seiko Okamoto came in leading the head-to-head 3–1. Chiaki Okadaue narrowed the head-to-head to 3–2.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2009-02-09 | Mildura 25K | R32 | grass | Seiko Okamoto | 6-1 1-6 6-1 |
| 2008-09-01 | Tsukuba 25K | R32 | hard | Chiaki Okadaue | 6-4 2-6 6-0 |
| 2006-10-30 | Sutama 25K | R16 | clay | Seiko Okamoto | 6-4 6-1 |
| 2006-10-16 | Makinohara 25K | QF | carpet | Seiko Okamoto | 6-4 6-4 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.