Seiko Okamoto defeated Junri Namigata 6-3 0-6 6-4 in the Nagano 25K quarter-final on carpet. The upset overturned the form book — Junri Namigata came in leading the head-to-head 4–1, but Seiko Okamoto had been the form player, winning 4 of their last 8 on carpet. Seiko Okamoto narrowed the head-to-head to 4–2.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2009-05-11 | Kurume 50K | R32 | grass | Junri Namigata | 6-3 6-1 |
| 2007-10-29 | Taoyuan 50K | R32 | hard | Junri Namigata | 6-3 6-3 |
| 2006-09-25 | Tokyo 50K | R16 | hard | Junri Namigata | 6-4 2-6 6-1 |
| 2005-05-30 | Gunma 25K | QF | carpet | Seiko Okamoto | 3-6 6-1 6-3 |
| 2005-04-25 | Hamanako 25K | R32 | carpet | Junri Namigata | 6-3 6-3 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.