There were really a lot of great matches this year, but the one that I probably won't forget for a while is the Sanguinetti vs Srichaphan match. I only saw the last set of that match, but that was already enough. Not only did both men saved some incredible points on their serve to get to the breaker, but some more insane points in the breaker.
The reaction from the players played a huge role too: Srichaphan lying on the ground then turns around and does a few push-ups; Sanguinetti and Srichaphan both kissing the net; lob shot on break point against Sanguinetti's serve or something, then Srichaphan attempts a backhand crosscourt backhand passing shot and that clipped the tape to go over the net to give him another break point, etc.
All in all I think that was the best match I have seen during this USO.