Instead of giving a simple prediction about Pacquiao-Mosley, here is my opinion on the range of possible outcomes for the fight. Envision these different scenarios as parts of a pie chart, or a specific confidence level in each outcome.
Scenario 1. Pacquiao defeats Mosley by wide decision. 55%
In this scenario, Pacquiao pulls ahead with a commanding performance against Mosley. It's possible that Pacquiao even scores a knockdown or two. In this scenario, expect Pacquiao to win at least nine rounds, which would be 117-111. I don't think Pacquiao will win every round in the fight. Sometimes he takes his foot off of the gas pedal, granting mercy on his opponents (think Clottey or Margarito), but he should clinch the victory comfortably in this scenario.
Scenario 2. Pacquiao defeats Mosley by late-round stoppage. 25%
Similar to Pacquiao-Cotto, the fight ends on an accumulation of punishment. Mosley's corner throws in the towel or Shane himself refuses to come out for the bell during one of the championship rounds. There could also be a knockdown or two in this scenario. For this particular outcome to occur, Pacquiao would have administered a savage beating on Mosley.
Scenario 3. Mosley defeats Pacquiao by early-round knockout. 10%
Mosley's best chance to win the fight may be in the early rounds, similar to the Mayweather fight. If Mosley can land something hard early, before Pacquiao is into the fight, he may have the chance to get him out of there. Pacquiao does temporarily pause sometimes after he is hit with good shots. Expect a Mosley lead or counter right hand to start the damage.
Write this down: At some point, Mosley will land something hard. Pacquiao likes to feel his opponents' power in the early rounds of a fight. Also, Pacquiao's defense is certainly not on the same level as that of Floyd Mayweather, Jr. If Mosley hurts Pacquiao, he has to knock him out immediately. Pacquiao and Freddie Roach won't give Mosley too many opportunities.
Scenario 4. Pacquiao defeats Mosley by early-round knockout. 5%
This scenario would most resemble the third Pacquiao-Morales fight, where Pacquiao's hand speed and power would be too much for Mosley to take. In Pacquiao-Morales III, Morales refused to continue, realizing it wasn't going to be his day. If Mosley's timing and reflexes are shot, then this scenario could occur.
However, it's particularly difficult to envision Mosley refusing to continue. (Of course, I realize that the same could have been said about Morales.) Mosley has never been knocked out and takes pride in his chin. He knows that this is his last big opportunity; there is no "live to fight another day."
Scenario 5. Other. 5%
The "Other" category covers a draw, a close decision victory for either fighter, mid or late-round knockouts by Mosley, a technical decision because of a head butt or injury, or a no-contest because of an early-round head-butt. Individually, these "Other" scenarios are not likely, but, in aggregate, they are all possible and must at least be presented as potential outcomes of the fight.
Pacquiao wins by 118-109, with Mosley winning two rounds and Pacquiao scoring one knockdown.