Manny Pacquiao put on a dazzling display in his return to the ring after a brief retirement, scoring a unanimous decision over champion Jessie Vargas to claim the WBO welterweight title in Las Vegas on Saturday.

Despite giving away 10 years to his opponent, the 37-year-old Pacquiao fought with more intensity and energy, and dominated the American in the final rounds to close out an emphatic victory.

The judges scored the bout 114-113, 118-109 and 118-109 in favour of Pacquiao, the only fighter to hold titles in eight divisions, with the Filipino improving to 59-6-2, while Vargas fell to 27-2.

It was a master class taught by the first sitting Senator to win a world boxing championship as Pacquiao temporarily left the ring to win election in the Philippines and serve in office before making a return to what he called his "passion".

Pacquiao, whose last previous bout was a unanimous decision over Timothy Bradley in April, showed quickly that he had not lost his skills, knocking Vargas down in the second round with a straight left to the champion's face.

Vargas battled back and landed his dangerous right several times but Pacquiao withstood the punishment and by the end of the bout, the American's face was swollen on one side and he had a cut over his right eyebrow.

The Filipino southpaw piled up the points in the later rounds by peppering the title holder with stiff right jabs that set up his quick, punishing left hook.

"I feel happy," said Pacquiao, whose only regret was in not recording his first knockout victory since 2009. "I feel like I could do more but my aim in every round is not to knock him out.

"Thanks to all my fans! Thanks to all the Filipino people!" he added in the ringside interview.

Among the spectators at the Thomas & Mack Center were the currently retired Floyd Mayweather and light-welterweight champion Terence Crawford. Pacquiao lost the richest bout ever to Mayweather last May.

"Next? I'm going back to the Philippines to work in the Senate," Pacquiao said about his immediate plans before being asked about Mayweather or Crawford.

"I don't know, whoever the people wants to fight me. Whoever my promoter gives to me, I will fight."

Vargas described the bout as "a chess match".

"It was interesting for me. We were on our toes trying to catch a big shot. He caught me a couple of times, I caught him a couple of times. It was an entertaining fight," he said.

"It's a good learning experience being against one of the best such as Manny Pacquiao. This automatically elevated my game and I know I have more potential."

Earlier, undefeated 25-year-old Mexican Oscar Valdez Jr (22-0) topped the undercard with a brutal seventh-round stoppage of Japan's Hiroshige Osawa (30-4-4) to retain his WBO featherweight championship.