ARLINGTON, Tex.  As Manny Pacquiao bruised, bloodied and disfigured the face of Antonio Margarito late Saturday inside a boxing ring at Cowboys Stadium, he turned a far larger man into another small obstacle on his march toward history.

Against his biggest opponent yet, in his eighth weight division, Pacquiao did what Pacquiao always does: he dipped and danced and fired southpaw, he ducked and spun and landed a tornado of combinations. When it ended, Pacquiao had earned his 13th straight victory and the World Boxing Council’s vacant 154-pound title, in a bloodbath, by unanimous decision.

“I can’t believe I beat somebody this big and this strong,” Pacquiao said.

With each round, Margarito’s face worsened, as if Pacquiao was painting a brutal boxing masterpiece. It went like this: seventh round, left eye closed; eighth round, bleeding from nose; ninth round, left cheek bruised; 10th round, fight nearly stopped.

In the 11th round, Pacquiao glanced at the referee, almost pleading for a stoppage. In the 12th, he took mercy, punching rarely, allowing Margarito to finish on his feet, after which he was taken to the hospital.