Mark Nielsen defeated Michihisa Onoda 6-4 7-6 in the Japan F6 qualifying round on hard. The upset overturned the form book — Michihisa Onoda came in leading the head-to-head 2–0. Mark Nielsen claimed a first win over Michihisa Onoda in three meetings, narrowing the head-to-head to 2–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2004-09-06 | Japan F7 | QF | hard | Michihisa Onoda | 6-3 6-1 |
| 2004-04-12 | Japan F1 | SF | carpet | Michihisa Onoda | 6-2 6-2 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.