Jeff Horn’s defeat of world champion Manny Pacquiao left the world of boxing stunned as he grabbed the World Boxing Organisation welterweight crown on Sunday.

Jeff Horn, nicknamed "The Hornet", grew up in Brisbane and first walked into a boxing club 11 years ago to learn self-defence.

On Sunday he won a brutal fight, in front of a packed hometown crowd at Brisbane's Suncorp Stadium, despite a controversial unanimous points decision, with the three judges scoring the fight 117-111, 115-113 and 115-113 to the Australian after 12 rounds.

Pacquiao's camp slammed the officials after the Filipino lost his World Boxing Organisation welterweight title.

"The referee was sketchy, the judges were crazy," said Pacquiao's strength and conditioning coach Justin Fortune, who is a former Australian heavyweight champion.

"Manny lost the fight but Jeff Horn looks like a pumpkin," Fortune added, referring to Horn's ending the fight with a badly swollen face and needing stitches over his right eye.

A 2012 Olympian, Horn's best win had come against faded former world titlist Randall Bailey and it was widely believed facing Pacquiao would prove too much of a step up.

It was a notion Horn, who worked as a substitute teacher in the early stages of his professional career, was keen to disprove as he showed his aggression early on.

Pacquiao opened up a cut over Horn's left eye in the third round but the Filipino was left bloodied himself following accidental clashes of heads in the sixth and seventh rounds.

Horn troubled the overwhelming favourite over the middle part of the fight but Pacquiao was beginning to warm to his task in the eighth and a ferocious assault in the ninth seriously wobbled his opponent.

Having somehow stayed on his feet, Horn kept pouring forwards but it was Pacquiao who was on top over the closing stages of a scrappy contest, only for the judges to side with the challenger.

Fortune, who once fought against Lewis and has been with Pacquiao since 2002, said Horn had been allowed to get away with a host of illegal tactics as he brawled his way to victory.

"That's what you get down here," he said of the tactics. "You'd never get away with that anywhere else in the world. You'd be penalised points. I don't have a problem with dirty fighting and that's what it was, a fight. You do what you have to to win."