Ai Sugiyama defeated Steffi Graf 6-4 1-6 7-5 in the San Diego round of 16 on hard. The upset overturned the form book — Steffi Graf came in leading the head-to-head 4–0. Ai Sugiyama claimed a first win over Steffi Graf in five meetings, narrowing the head-to-head to 4–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 1999-03-05 | Indian Wells | R16 | hard | Steffi Graf | 6-0 6-1 |
| 1999-01-11 | Sydney | R32 | hard | Steffi Graf | 6-0 6-4 |
| 1998-11-02 | Leipzig | R16 | carpet | Steffi Graf | 6-4 6-3 |
| 1998-03-05 | Indian Wells | R16 | hard | Steffi Graf | 6-0 6-1 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.