Guillermo Bujniewicz defeated Federico Delbonis 6-4 6-2 in the Argentina F6 qualifying round on clay. The upset overturned the form book — Federico Delbonis came in leading the head-to-head 2–0, but Guillermo Bujniewicz had been the form player, winning 4 of their last 8 on clay. Guillermo Bujniewicz claimed a first win over Federico Delbonis in three meetings, narrowing the head-to-head to 2–1.
| Date | Tournament | Round | Surface | Winner | Score |
|---|---|---|---|---|---|
| 2009-05-25 | Argentina F7 | R32 | clay | Federico Delbonis | 6-4 6-1 |
| 2008-07-21 | Paraguay F3 | R32 | clay | Federico Delbonis | 6-1 6-3 |
Averages over each player's completed matches in the selected window. ATP, WTA & Challenger.