After seeing both fights against Mosley, it's obvious why Mayweather refuses to fight Pacquiao. Meriweather was just too fast for Mosley. Mosley never feared getting hurt much less knocked down by Meriweather but he couldn't get much leather on him aside from that one round where he hurt Floyd. Pacquiao on the other hand was not only faster (and Manny wasn't his usual quick self moving laterally) but so much more powerful. Mosley knew that Manny could not only hurt him but knock him down with one punch. Like the other Pacquiao opponents, Mosley felt his power and fought scared and defenslvely the rest of the night just trying to survive.
Before tonight I thought a Pacquiao-Mayweather fight would be close but not anymore. Fast vs Fast and Powerful isn't a contest. Mayweather can't hurt Pacquiao at all but Pacquiao can kill Mayweather.
If it didn’t work in Phoenix with Nash and Stoutamire... it’s just not a winning formula. It’s an entertaining formula, but not a winning one. - Derek Harper talking about D'Antoni's System