Name some past greats who were extremely adept at fighting while clearly tired. I'd say almost all great fighters have this ability to some degree, but who stands out in your mind? Ali obviously, SRL, Duran... recently I think of Toney and Morales immediately. Who else?
Zsolt Erdei. Watch his fight with Fragomeni. He outboxed him for the first four rounds, than was already totally spent - he took on Fragomeni on 3 weeks notice and was ill with the flu for one week of those three - but managed to win the brawl with the 20 pounds heavier man.
Salvador Sanchez. The way he maintained his accuracy and composure in the final rounds against Azumah Nelson was exceptional. Sanchez had eaten some serious leather and fought at a horrid pace throughout, and Nelson didn't seem to have an ounce of quit in him. If you didn't know the result beforehand, I think that approaching the championship rounds you would think Sanchez would be the one to break. The way he pushes through the fatigue to end it is just awesome.
Pedroza was excellent in the late rounds. Arguello paced himself well. Fenech at his best. But Armstrong prolly stands above all others for mine. The obvious answer for me.
Ali and Frazier were both spent in their third fight but both managed to keep the action ferocious. Duran was pretty tenacious even when fatigued.