Manny Pacquiao stopped Erik Morales in the third round in the third meeting between the super featherweight rivals.
Morales first hit the canvas in the second round
Filipino Pacquiao put the three-time world champion on the canvas three times in Las Vegas as he earned his 34th win inside the distance.
It was 30-year-old Morales' fourth defeat in his past five fights.
WBC International super featherweight champion Pacquiao lost on points to Morales last year but stopped the Mexican in the 10th round last January.
Southpaw Pacquaio now has 43 wins, three defeats and two draws, while Morales (48-5) once again failed to arrest the slide in his glittering career.
Both fighters came out blasting and Pacquiao first knocked Morales down against the ropes late in the second round.
Morales kept returning shots, but couldn't keep up with Pacquiao's pace - and after a knockdown midway through the third, Pacquiao finished him with a devastating left hook with just three seconds left.
I was hurt by the power of his punches, and maybe it's time to think about not doing this anymore
"He was coming to me, and he was not able to handle me," Pacquiao said.
"I felt so much stronger than him. I was prepared to fight the best of Morales."
Afterward, Morales acknowledged he might be finished after 52 brutal fights, including four losses in his last five.
"For the first time in my career, I actually felt the power of an opponent like I've never felt it before," said Morales, who also lost two of three fights in his previous trilogy against fellow Mexican Marco Antonio Barrera.
"I was hurt by the power of his punches, and maybe it's time to think about not doing this anymore. I had a great career. Maybe it is time."
The fighters split their first two meetings, with Morales winning a unanimous decision in 2005 and Pacquiao replying with a TKO victory over 'El Terrible' in January.
Thousands of Filipino fans travelled halfway across the world to Las Vegas for the fight, while thousands more came up from Mexico and Southern California to support Morales.
The crowd of 18,276 was the second-biggest in the Thomas and Mack Center's history.
On the undercard, Colombia's Ricardo Torres won the WBO light welterweight title with a split decision over Mike Arnaoutis of Greece.
Mexico's Omar Nino retained his WBC light flyweight title with a majority draw over former champion Brian Viloria of the Philippines, even though Viloria knocked down Nino twice.