Khan wasn't a massive (or particularly durable - and no I don't buy he was all that drained) lightweight. Margarito was essentially a natural big light middleweight (or even regular size middleweight) who made his name bullying welterweights. He relied on size and chin (and in some instances maybe plaster) to break guys down, while struggling and displaying his actual mediocrity at his natural weight classes where he probably always belonged. I don't rate Margarito or anything, but he positively manhandles Khan if we're talking about 147lbs here, as you presumably must be. Margarito was a JCC Jr. style giant bully at the weight, and Khan is a weak-chinned blown up lightweight who got bullied a bit in his one sojourn to welterweight by Kidd Diaz.
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Guys who take PEDs let alone are shameless to put plaster on their fists shouldn't be given any credit. I have more respect for guys like Ortiz Khan Cotto than Berto Pederson Margacheato
Khan is not knocking Margarito out, and is not near durable enough to last 12 rounds with him.. There is literally no chance for Khan.