Juan Manuel Marquez overcame eight years of frustrations and three disputed results with one crushing punch.

Never had Manny Pacquiao looked so vulnerable and fallen. Lying on the canvas face-down, Pacquiao became a knockout victim instead of usual conqueror against his familiar nemesis.

Marquez, 39, finally avenged two previous losses and a draw to Pacquiao with a sixth-round knockout victory in their welterweight bout late Saturday in Las Vegas.

“I felt great and prepared very strong,” Marquez said. “I knew it was going to be a difficult fight but not impossible to win.”

Just as Pacquiao was building a lead on the scorecards with a knockdown in the fifth round and a solid sixth, Marquez found his opening — which ended Pacquiao’s night. In the closing seconds of the sixth, Pacquiao lunged at Marquez, who slipped a right hand and countered with a devastating short right to Pacquiao’s chin.

Pacquiao fell face-first toward the ropes and remained motionless for a few seconds. Referee Kenny Bayless waved the 10-count, ending the fight at 2:59 of the round.

“An important point was combining aggressiveness with technique,” Marquez said. “We didn’t allow Manny to connect as he usually does.”

Marquez (55-6-1, 40 KOs) reminded Pacquiao that their fourth fight had a different tone when he floored Pacquiao with a right to the head in the third round. Marquez had never knocked down Pacquiao in their three previous bouts, while Pacquiao sent Marquez to the canvas four times.

On Saturday, Pacquiao (54-5-2) again knocked down Marquez with a left to the head in the fifth and hurt him later in the round with a solid right to the head.

But Marquez, bleeding from the nose, shook off the knockdown and Pacquiao’s shots in the nearly-completed sixth round. Ending the fight within 12 rounds spared Marquez the torment of dealing with the judges’ verdicts. At the time of the stoppage, Pacquiao was ahead, 47-46, on all three scorecards.

“I thought I had him the last couple of rounds but I started getting overconfident,” said Pacquiao, who underwent a precautionary CT scan at a Las Vegas area-hospital after the fight. “I got careless with that punch. I was so overconfident. I thought I had him.

“He is one of the top boxers. He’s not an easy fighter to beat. I did my best but that’s boxing — that’s sports.

“I want to congratulate Juan Manuel. I have no excuses. It was a good fight and he deserved the victory.”

Gamboa wins

Miami resident Yuriorkis Gamboa won a unanimous decision against Michael Farenas in the bout preceding the Marquez-Pacquiao fight late Saturday.

Gamboa (22-0) knocked down Farenas (34-4-4) in the third and seventh rounds but could not finish him within the distance. Farenas floored Gamboa in the ninth, but Gamboa shook off the knockdown and re-established the pace in the final three rounds.

All three judges scored the junior-lightweight bout for Gamboa, 117-109, 118-108 and 117-108. The fight was Gamboa’s first after a 15-month absence.

Johnson not done

Delay the Glen Johnson retirement a bit longer. Johnson, the Miami resident, who talked about retiring if he failed to win his previous fight, is not ready to leave the ring just yet.

Johnson, who turns 44 in January, will face unbeaten prospect George Groves on Saturday in Groves’ native England. Terms of the scheduled regional super-middleweight title bout were finalized three weeks ago, according to Johnson’s longtime manager, Henry Foster.

“I was training off and on and told Henry if the opportunity came up, we’ll go for it,” Johnson said. “After I started training, I noticed some loopholes that affected me in my last fight.”

In the days leading to his bout against Andrzej Fonfara on July 13, Johnson said he could not envision fighting again unless he defeated his Poland-born opponent. Fonfara won a unanimous decision, giving Johnson (51-17-2, 35 KOs) his third consecutive loss.

“It was a tough loss; I had to question what was going on,” Johnson said. “I didn’t think [Fonfara] was one guy that was going to stand out in the sport. I still have the passion for the sport and like the challenge boxing brings me.”

The 24-year-old Groves is 15-0 with 12 knockouts.

Johnson appeared on the last fight televised by CBS on a weekend afternoon. Fifteen years after Johnson’s unsuccessful middleweight title bid against Bernard Hopkins, CBS once again will showcase boxing during afternoon programming.

CBS will televise the International Boxing Federation bantamweight title fight between defending champion Leo Santa Cruz and challenger Alberto Guevarra Saturday afternoon from the Sports Arena in Los Angeles. The telecast also will feature the professional debut of 2012 U.S. Olympian Joseph Diaz.