According to Pacquiao, it was mercy:

 

Class act and premier warrior that Pacquiao.

He admitted Margarito hurt him pretty good in the middle rounds. I don't know why Margarito didn't have the killer instinct he usually shows in the ring. Was also surprised that Manny was able to get Margarito wabbly, never thought he had the power to hurt a guy as big as Margarito.

 

margarito looked tried after 3 rounds. margarito didn't look like he had the foot speed. i think he had probably only 3 to 4 good exchanges by getting manny against the ropes the entire fight. manny was just too quick and his hand speed killed margarito. and margarito isn't known to be an accurate puncher and he just brawls with his opponents. the only time margarito had success in his past fights is when the opponent stands toe to toe with margarito and exchange punches. manny was too smart for that. 3-4 combos and move around - wash, rense, and repeat.

people said margarito had length and was bigger. thing is, margarito is a different type of fighter. i saw his jabs - slow and with no power in them. he doesn't know how to use his size to fight on the outside. instead he pressures you against the ropes and corners. no way manny would let him do that.