LAS VEGAS — Vindication was extra sweet for Juan Manuel Marquez Saturday when his stunning knockout of Manny Pacquiao in the sixth round of their non-title welterweight bout earned him his first victory over the Filipino in four meetings. The Mexican had been determined to set the record straight against the Filipino southpaw, having previously lost twice and drawn once. He believed he had been “robbed” by the judges in the previous fights. Pacquiao was first knocked down in the third round but sent Marquez to the floor in the fifth and looked to be getting the better of the scheduled 12-round fight until he missed with a right and was stunned by a thunderous counter-punch. The Filipino southpaw fell face first and lay motionless for a couple of minutes before being helped to his corner where he sat on a stool as his gloves were removed. “I am very happy with this victory,” a jubilant Marquez told reporters after flooring Pacquiao just one second before the end of the sixth round at the MGM Grand Garden Arena. “I feel so, so happy. I am very happy that I didn't retire last year. Now I feel great that I leave no doubt in the way that I got this victory over Manny.” A fuming Marquez had contemplated retirement after losing a controversial majority decision to Pacquiao 13 months ago at the same venue, firmly believing he had once again been cheated of victory. The Mexican had said at the time: “It's hard when you're fighting your rival and the three judges too. I got robbed.” However, Marquez refused to quit. He returned to the ring in April and beat Ukrainian Sergey Fedchenko on an unanimous decision to win the WBO light welterweight title before setting his sights on a triumphant fourth meeting with Pacquiao. “I knew Manny could knock me out at any time. I threw a perfect punch,” said four-division world champion Marquez, who had his nose broken by Pacquiao. “We always worked on that (counter punch),” added the Mexican. “We knew he was going to come out aggressive so we had a fight plan that was more technical. We were able to capitalize on it. I put this fight as one of my greatest victories. “This is the result of all the hard work that I did,” the Mexican smiled after improving his record to 55-6-1 with 40 knockouts. “I put this fight as one of my greatest victories absolutely. “Right now in my future I don't know what is coming, but I am going to celebrate with my family and my friends in Mexico.” While the 39-year-old Marquez is no rush to plan his next move as a boxer, Pacquiao's illustrious career stands at a crossroads following his second successive defeat this year. The 33-year-old Filipino, who has won world titles in an unprecedented eight weight divisions, was taken to a Las Vegas hospital as a precaution. Before leaving the arena, Pacquiao suggested he would be keen to take on Marquez for a fifth time but his trainer Freddie Roach was uncertain. “Possible retirement, possible re-match,” the bespectacled Roach said. “I would love to get a re-match but is that the best move? I'm not sure which way we're going to go right now. “It really depends upon how he feels and what he wants to do. I'll definitely tell him to retire if he's not able to do it in the gym, but we have to see.” Asked to assess what had happened to Pacquiao, who had been leading 47-46 on all three judges' cards when the stoppage came, Roach replied: “I thought Manny was having a good fight. He ran into a good one. I thought we almost had him. Manny got a little careless and then he ran into that punch. He fought a very smart opponent. I hate to lose.” — Reuters