You are probably thinking, this guy must be smoking some of the most mind-altering substances known to man to make this type of a proclamation. Well, allow me to present some facts and theories to further explain my reason for saying such a thing.
Take a look at the profile of the boxers that Shane Mosley has lost to in his career. Shane has six losses to four different guys. The late Vernon Forrest, who was a tall, jab-dominant fighter who was able to neutralize Mosley's speed with his accurate and strong jab. Winky Wright, another taller welter/middleweight fighter, with a better than average jab. Most importantly, Winky's fight game is all about defense. Floyd Mayweather Jr, one of the best defensive fighters of his era, also completely outclassed this late-30s version of Mosley. You see the common theme here. Shane likes to press the action, fighters that give him an issue are usually guys that have a way to slow his pursuit down. They disturb his rhythm, either with the jab or causing him to miss his straight right leads, presenting counter opportunities.
The only exception to this rule was Miguel Cotto. Cotto is always easy to hit, I believe Mosley actually won this fight or drew at best. It was an exciting fight, though, and was disputable. I believe that Pacquiao's hard charging style gives Mosley an advantage. He will not have to find Manny, he'll be there for him to hit. This leads me to my next point.
Lets not forget Manny's chin is what I would grade as decent. Not granite, not glass, but decent. Pacquiao has been stopped twice, granted it was early in his career, in a smaller weight class. Since he's moved up, he hasn't been stopped or down since then. Shane has never been stopped. Pacquiao admitted he was hurt from body shots from Margarito. Any one that has seen Margarito fight knows he is slow and methodical. Comparatively, Mosley is much quicker, with a longer reach than Margarito.
If Shane can use his jab to slow Manny's charge and gets in close to use his size and strength to bully Pacquiao, he may be able to control him physically. One concern that could derail my prediction is that Shane has been careless in recent fights, holding his left hand too low. If he does that against Pacquiao, he'll get hurt.
If he can establish the jab early and incorporate the straight right follow and counter off of Manny's misses, he can catch Manny.
Since Manny has been fighting at 147 or higher, his competition has been a bit suspect. An over-the-hill De La Hoya, a battered and beaten Miguel Cotto, psychologically scarred by Margarito and his plaster-laced hand wrap. A seemingly disinterested and afraid Joshua Clottey, an overrated and ballooned-up lightweight named Ricky Hatton. One concern is that Shane may fall into the De La Hoya category, but if he has taken stamina and patience into strong consideration, he has a shot.
Importance of the Fight
Does this fight mean to Pacquiao what it means to Mosley? Manny wants Floyd, he feels that this fight will cement his legacy and make him an even more ridiculously-rich man than he already is. Shane is not Floyd, he's a consolation prize. How many of these types of fights will Manny be able to get up for, when he has to be doubting whether he'll ever get a shot at "Money," pun firmly intended.
For Mosley, this is it for him. This is the last truly meaningful fight he'll have if he loses. Mosley loves the sport and he loves competing. He is one of the proudest athletes in my recent memory.
If Manny isn't sharp, Shane will capitalize. I acknowledge there are a healthy amount of "ifs" required for Shane to pull this upset. I also recall there were a lot of "ifs" required on a February night in Tokyo, Japan in 1990. Those "ifs" became reality on that night and Buster Douglas defeated Mike Tyson. Breidis Prescott floored Amir Khan to hand him his first loss. Corrie Sanders flattened Wladimir Klitschko to hang an "L" on the big Ukranian.
Would this be a bigger upset than any of those fights? Shane is a future Hall-of-Famer, dangerously close to 40 years old. It is not impossible that he could pull the seemingly impossible tonight.