In the first round, Rios adopted the Juan Manuel Marquez strategy of hanging back and looking for the right hand counter but lacking the Mexican icon's quickness and precision counter-punching abilities, was on the receiving end of Manny Pacquiao left hands to the head and body.
Brandon Rios reverted to his normal form in the second, inching forward behind a high guard and whaling away at Pacquiao anytime he got close. This presented Pacquiao with ample opportunity to whip hooks around the guard of Rios or stick in sharp body shots, but it also allowed Rios to score with hard shots on the inside as he mauled the much smaller Filipino at close quarters.
By the final minute of the second, a fluid, brawling battle broke out, the kind of approach that Rios favors but unfortunately for the American, one that the quicker Pacquiao is better suited for. Rios did keep Pacquiao honest however, as anytime the former multi-weight champion took a breather, he was hit by his adversary.
Rios started the third mixing what he did in the first two rounds, as Pacquiao looked to keep his distance and moving following his taking some unnecessary punishment from Rios in the previous frame. Pacquiao won the round by punching and moving but was caught a few times by his motivated rival, who was then shaken by a bracing counter in with 30 seconds left in the third.
The fourth saw Rios apply a lot of pressure with Pacquiao landing a few eye catching shots that snapped back the head of Rios but the Californian hammered "Pac Man" in the clinches and the smaller man was affected by a spearing body shot from Rios later in the round.
By the fifth, Rios had largely abandoned jabbing his way forward and was no longer circling away from Pacquiao's left and as a result was punished, absorbing several full-blooded left hands to the face and furious head-body combos from Pacquiao. Rios only had success in the clinches with clubbing, one handed shots.
Rios discovered the jab again in the first half of the sixth, disrupting Pacquiao's flow somewhat and allowing for some effective offensive forays. But Pacquiao soon realized perhaps his best defense would be to go offensive and he went on a tear, throwing a high volume of punches, some of which got through but also effectively causing Rios, who was by now cut above the left eye, to shell up and stop throwing.
The seventh was target practice for Pacquiao as he maintained distance from Rios and picked him apart. Whenever Pacquiao took a second to stop and clinch or just slow down, Rios was on him throwing punches but not much got through.
Pacquiao outboxed Rios in the eighth but took his foot off the gas, content at times to trap Rios' left arm in clinches and allow himself to be clubbed by the right, just to take a breather. Rios was more active, employing the jab and throwing a hail of leather whenever he came to grips with his fleet-footed opponent but Pacquiao went on a tear in the last 30 seconds, scoring at will.
The ninth was much like the eighth but with less clinching and minus the late Pacquiao rally. As usual when Pacquiao slows down a bit, Rios did a better but was starting to show signs of the punishment he'd taken, particularly around the eyes.
Rios was clearly tired in the tenth, looking dispirited after getting told off by referee Genaro Rodriguez, and was belted around by the more energetic Pacquiao. The eleventh was another field day for Pacquiao but Rios made more of an effort and as a resulted, landed a few good shots.
With Rios probably having lost every round, going into the 12th, he would need a knockout in order to win but taking a lot of punches for all eleven of the previous rounds had left him unable to mount anything different than what he had done in the eleventh.
Pacquiao was awarded a well-deserved 120-108, 119-109, 118-110 unanimous decision victory, snapping a two bout losing streak and improving to 55-5-2 (38). Rios loses his second bout in a row, dropping to 31-2-1 (23), but showed a granite chin and tremendous will as he never stopped trying against an opponent of superior abilities.
Chief support was provided by a rematch for the IBF featherweight crown with Evgeny Gradovich, 18-0 (9), improving on his split decision title win earlier this year against Billy Dib, 36-3 (21), by stopping the Aussie at 1:10 of the ninth.