Jeff Horn claimed a stunning and controversial upset win over Manny Pacquiao to become the new WBO welterweight champion on Sunday.

Not many believed Horn could beat Pacquiao and even after the fight at Suncorp Stadium in Brisbane was over, most were willing to give the Australian credit for giving his legendary opponent a tough fight.

Then the decision from the judges came – a unanimous decision for the new WBO welterweight champion – as Horn was declared the winner in a stunning upset.

The judges scored it 117-111, 115-113 and 115-113 in Horn's favour.

The 29-year-old Horn came out as the aggressor, but appeared to wilt in the middle rounds as Pacquiao was the better tactician and landed far more punches than Horn.

The controversial victory moves Horn, who has never fought outside of New Zealand or Australia, to 17-0-1.

He even called out undefeated Floyd Mayweather Jr. following the fight, holding a pair of boxing gloves in one hand and a "walking stick" in the other and asking Mayweather which would it be.

The Australian fans, most of whom supported their countryman, were treated to an action-packed first round as Horn was the aggressor early. But his aggression also left him vulnerable and Pacquiao caught him in the third to cut Horn above his right eye.

An accidental headbutt in round six resulted in a cut on Pacquiao's hairline, but the fight continued following a brief stoppage as Pacquiao was examined. That cut was on the right side of Pacquiao's head, but another headbutt initiated by Pacquiao in the seventh round resulted in blood gushing from the left side of his head.

Pacquiao, who was gracious in defeat, said the cuts on his head probably influenced the judges' decisions.

Horn came out firing in the ninth round, going right after Pacquiao, but he quickly slowed. By the end of the round, Horn's legs were wobbling and the right side of his face was covered with blood. That led to referee Mark Nelson telling Horn he was ready to stop the fight if Horn continued to take abuse in the 10th round.

Though Horn may have called out Mayweather, he did say he would love a rematch with Pacquiao and the 38-year-old Filipino said he was willing.

Even if Horn had not won the fight, he still would have won the respect of those who did not think he could go the distance with the 11-time world champion.

Controversial as it may be, Horn is still the new WBO champ thanks to his strong showing in the final three rounds after Nelson said he was ready to stop the fight.