By Mark Lamport-Stokes
Boos rang out from the crowd in the MGM Grand Garden Arena but Mayweather, who improved his career record to 42-0 with 26 knockouts, was unrepentant.
"I got hit with a dirty shot, I was protecting myself at all times," the 34-year-old said ringside. "I hit him with a left and then a right hand, and that ended the bout."
Asked to describe what happened as a replay of the final moments was shown on a giant television screen above the ring, Mayweather replied: "We touched gloves, right hand and that's all she wrote.
"You just protect yourself at all times. I was victorious. If he wants a re-match, he can get a re-match."
Mayweather then showered his interviewer with abuse and said he had never given him "a fair shake."
Ortiz responded with a furious sequence of blows before pinning the challenger to the ropes.
(Editing by Peter Rutherford)