The 35-year-old Argentine, who came in with a reputation as a big puncher, had no answer to Pacquiao's blistering speed and he dropped again in the fifth.
"I'm surprised I knocked him down so early -- in the third, fifth and seventh.
"We did a good job in training. We were not pushing hard -- we controlled our pace and ourselves.
"I'm no longer young, so thanks to my trainer and all my team members." A shell-shocked Matthysse, who had come in with a record of 36 knockouts in 39 wins with just four defeats, conceded he had no answer to Pacquiao's speed, movement and power as the "old Manny" returned with a vengeance.
"It's most difficult to be fighting Manny Pacquiao," he said. "He's a great fighter. I lost to a great legend."
- 'First step to a dream' -
On a great morning in Malaysia for fighters for the Philippines, Jhack Tepora earlier stopped Mexico's Edivaldo Ortega to win the interim World Boxing Association featherweight title.
Tepora unleashed a wicked short right hand in the ninth round to knock down Ortega for the first time in what had been to that point an even contest.
He swiftly followed up with a barrage of powerful swinging punches that forced the referee to step in after 2min 38sec of round nine.
Tepora cited Pacquiao as his inspiration. "When I saw Manny's story, coming from the streets, I thought one day I could be like that and this is the first step to that dream," he said.
Lu Bin's brave bid for a record world title win in just his second professional fight came crashing to earth when he was knocked out in the dying seconds of his battle with experienced WBA light flyweight champion Carlos Canizales of Venezuela.
Lu was felled near the end of the 11th round for the first time in his short pro career.
Canizales went for the kill in the 12th and final stanza. After a barrage of punches a storming straight right dropped Lu and the referee waved it off.
Moruti Mthalane from KwaZulu Natal in South Africa got off the canvas to take home the vacant International Boxing Federation flyweight title by outpointing Waseem Muhammad, who was bidding to become Pakistan's first ever world champion.
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)