It was the first action for Pacquiao since losing on points to Australian Jeff Horn in Brisbane a year ago.
As to what's in store for him, Pacquiao said there are many fights out there, mentioning Amir Khan, Terrence Crawford and Vasyl Lomachenko as possible opponents.
Pacquiao (59-7-2, 38 KOs), who turns 40 in December, takes his traveling road show to Kuala Lumpur, Malaysia, in a fight that should produce fireworks considering the power punching and brawling style of the 35-year-old Matthysse (39-4, 36 KOs).
A third knock down in the seventh round led Matthysse to spit out his mouthpiece, causing a frenzy among Pacquiao fans in the stadium.
Roach has been replaced for the fight by Pacquiao's long-term friend and cornerman Buboy Fernandez and another defeat could see the veteran "National Fist" hang up his gloves for good. "You have to rest and get it back and that's what I did".More news: Pence: 'Spurious Attacks On ICE By Our Political Leaders Must Stop'
His aggression knocked Matthysse down on one knee in the third and fifth rounds.
Duterte, who gave Pacquiao two thumbs up after the match, congratulated the senator for bringing pride to the Philippines and uniting Filipinos.
Pacquiao's knockout victory was a long time coming, said James Puebla, a nursing student.
It was a dominant, devastating display as Manny Pacquiao registered the 60th win of a fabled 23-year career.
Pacquiao has had issues with shoulder and calf injuries, although it seems that none of these have bothered the boxer in his fight with Matthysse as he even scored his first knockout win in nine years.
"You have proven time and again that you are not just a public servant, but one of the greatest boxers of all time", he said in a statement. South African Moruti Mthalane won a close twelve round unanimous decision over Pakistan's Muhammad Waseem to capture the IBF flyweight title.