Rewatching tua-oquendo

Man, big o was looking like Muhammad Ali in there. Moving his feet, fast combos, good reach, great defense with the foot work to back it up. My question is this: why was tua trying to be so defensively sound? Every punch fres threw at him affected him, nullifying his punching completely. When you watch guys like Marquez or Pacquiao they fire exchanges at the same time. Once in a while someone hits the deck Why couldn't tua just punch between the punches instead of getting hit by a power jab with no strength behind it??? This is the same way he fought Lewis, except fast fres is ten times less dangerous, nuff said.