Pacquiao knocked out by Marquez in sixth round
The 39-year-old Mexican, who had lost twice and drawn once in their three previous meetings, sent Pacquiao crashing to the canvas with a stinging right hand with one second left in the round.
Pacquiao, who had been knocked down in the third round, sent Marquez to the floor in the fifth and looked to be getting the better of the fight until the stunning knockout.
Promoter Bob Arum hinted at a fifth fight between the two.
"If they want to fight again, why not?" he said in a televised interview.