Australian Jeff Horn's shock welterweight title victory over Manny Pacquiao was confirmed on Tuesday after a scoring review by the World Boxing Organization declared him the clear winner.

The WBO took a close look at the fight after Pacquiao, backed by the Philippine government's sports regulatory body, criticised the referee and the judges and demanded a review after losing in Brisbane on July 2.

Horn stunned the Filipino legend — who has won world titles in an unprecedented eight weight divisions — with his ultra-aggressiveness to earn a unanimous 12-round decision.

The WBO — which does not have the power to reverse a decision unless fraud or law violations are proven — set up a panel of independent judges who were asked to watch the bout without sound and determine who won each round.

The results were tabulated to show clearly the rounds each fighter won using an average scale based on 60, 80 and 100 percent, with three of the five officials needing to be in agreement.

A similar method has been used to review WBO title fights before.

"Upon the analysis, the findings stated that Pacquiao won the 3rd, the 8th and 9th by 100 percent; the 5th round was won by 80 percent; and the 11th round by 60 percent," the WBO said in a statement.

"Horn won the 1st, 6th and 12th rounds by 100 percent; rounds 2, 4, and 7 by 80 percent; and then, the 10th round by 60 percent.

"From the results, it can be established that Pacquiao won five rounds while Horn won seven rounds. Based on this analysis, Jeff Horn was the winner of the bout."

Horn welcomed the review when it was announced, and said he was ready for a rematch, an option specified in the Brisbane fight contract.

"Let them review it," the 29-year-old told Queensland's Courier Mail newspaper.

"They will see it on a TV screen and probably see the same thing everyone else saw — me winning the fight."

Both the Philippine board and Pacquiao had criticised American referee Mark Nelson for supposedly allowing the underdog Australian to get away with illegal tactics without giving him warnings or point deductions.

The loss sparked calls in the Philippines for the 38- year-old Pacquiao, a national icon after rising from poverty, to retire and concentrate on politics.

Pacquiao briefly retired from boxing in 2016 to pursue his long-held political ambitions and was elected senator. But he quickly made a successful comeback against Jessie Vargas in November, saying he still felt like a youngster.