Chiaki Okadaue defeated Seiko Okamoto 6-4 2-6 6-0 in the Tsukuba 25K round of 32 on hard. 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 |
| 2008-05-26 | Gunma 25K | R16 | carpet | Chiaki Okadaue | 6-3 6-2 |
| 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.