I'm supposing you've only begun to watch boxing now. Mosley, one of the two best lightweights of the last 40 years? No. Just no.
Duran has a far superior resume at lightweight, and it was his best weight for head to head matches in theory. However I think they are probably the two best lightweights in history in terms of head to head match ups, NOT in resume, specifically of Mosley. I honestly do not think that any lightweight in history could beat Duran or Mosley on their best day at that weight. They were both physically massive for the division, had immense speed and power. I do not think that the Castillos, Corrales, Casamayors, Frietas, even Mayweather could be favored over these two. As for against eachother... I think its a pick em fight.
Knock him out ? I don't think so. Could Mosley beat him? Sure, but I would bet on Duran, Duran is the favorite in this one by far
http://www.eastsideboxing.com/forum/showthread.php?t=308494 Extremely tough fight for Duran in my opinion but he'll take a clear UD.
I wouldn't be surprised by a Mosley victory in a series of fights, but ultimately, Duran would get the better of him.
If you are looking to crush a 135 pound Roberto Duran the only thing I can suggest is an articulated lorry.