I don't think that pressing Mayweather and staying on him throwing punches is the way to beat him, generally because that is what he wants you to do. Throw punches that miss, get frustrated and throw more punches....all it does is make you easier to counter. Also, the advantage of being a southpaw is in the angles it creates. You give this away by being real close. I don't think that Ortiz punches that well close up- it seems to me that he needs some room.
I remember watching Mayweather/Judah, and Floyd didn't show me much, so far as his ability to attack a southpaw. He seemed to be limited, idea-wise, to jumping in behind lead right hands, then tying up. Ortiz can make his too-wide stance work for him, if he can entice Mayweather to lead, draw back to his left foot and counter. I don't belive that he is intelligent enough, boxing-wise, to fight Mayweather at his own game and win. He isn't that smart at trying to hit guys that don't want to get hit.
For years the 'book' on Toney was to get on him and keep punching and that got a lot of guys beat up. Same with Mayweather. The best shot is to make him lead, and Ortiz just ain't that smart.