Seiko Okamoto defeated Nungnadda Wannasuk 6-1 7-6 in the Hamanako 25K round of 32 on carpet. The upset overturned the form book — Nungnadda Wannasuk came in leading the head-to-head 1–0. Seiko Okamoto claimed a first win over Nungnadda Wannasuk in two meetings, narrowing the head-to-head to 1–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2009-09-14 | Kyoto 10K | QF | carpet | Nungnadda Wannasuk | 6-3 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.