Seiko Okamoto defeated Suchanun Viratprasert 6-4 0-6 6-0 in the Nuriootpa 25K round of 16 on hard. The upset overturned the form book — Suchanun Viratprasert came in leading the head-to-head 4–0. Seiko Okamoto claimed a first win over Suchanun Viratprasert in five meetings, narrowing the head-to-head to 4–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2009-08-31 | Tsukuba 25K | R16 | hard | Suchanun Viratprasert | 6-2 6-4 |
| 2008-07-14 | Miyazaki 25K | R32 | carpet | Suchanun Viratprasert | 6-0 7-5 |
| 2004-08-02 | Louisville 50K | R32 | hard | Suchanun Viratprasert | 6-1 6-1 |
| 2001-11-12 | Haibara 10K | SF | carpet | Suchanun Viratprasert | 6-2 6-1 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.