OK, even though it probably wouldn't be my first choice, one match I wish I could see the result changed of was Andre Agassi v Ben Becker at USO 2006.
I always felt that Agassi should have been retired by Roddick in the next round, it would have been perfect, the last all American encounter, passing of the torch in a way, one last marque match under the lights of NYC. The loss to Becker just felt wrong, felt like we were robbed of him getting that grand send off by going up against Roddick there.