It was Pacquiao's first victory inside the distance since 2009 and improves the eight-division world champion's record to 60-7-2.
Following his shock loss to Australian journeyman Jeff Horn last time out, Pacquiao chose to change his corner team, and his new line-up paid immediate dividends. I hope it is not the last fight under MP Promotions here, as this is one of the big fights in Asia, which was shown in more than 200 countries. "When you see me in training, you can tell I'm like 28, 27 years old", Pacquiao said.
Filipino boxing icon Manny Pacquiao is a world champion again.
"Right now, I'm happy to go back to my country and celebrate the victory".
Matthysse, known as "The Machine" for his aggressive punches, had claimed the vacant welterweight title in January after defeating Thailand's Tewa Kiram.
"Like I said, I'm not yet done".
"This is part of boxing".
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Pacquiao faced calls to retire from friends, family and even his Hall of Fame trainer Freddie Roach when he lost the WBO belt to journeyman Australian Jeff Horn a year ago.
Duterte said in a statement that Pacquiao has proven himself again as "one of the greatest boxers of all time" and that the win will cement his legacy in the sport.
It was Pacquiao's 39th KO win of his fabled 23-year career but his first since he beat Miguel Cotto in November 2009, nearly nine years ago.
Matthysse, 35, had won 36 of his 44 fights by knockout going into the bout. Venezuela's Carlos Canizales defended his WBA world light flyweight title against China's Lu Bin, stopping him from making history by becoming the first boxer to win a major world title in just two career fights.
"May you continue to inspire Filipinos not only in boxing but also in the public service", Duterte said.
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.