IMO, the best Sampress performance was QF 1996 US Open against Corretja.
I was sure he was going to lose going to the 5th set.
He looked weak,dizzy, vomitted a few times, and umpire called time on him.
Meanwhile Corretja was jumping up and down and looked really fit.
Somehow he manage to win , this was a heart of a champion, he went on to win easily in the finals against Chang.