Devin Haney underlined his status as the king of the lightweight division, beating George Kambosos Jr for the second time to retain his undisputed world titles in Melbourne.

The three judges all scored the bout in favour of the American, 119-109, 118-110 and 118-110, who retained his IBF, WBC, WBA and WBO belts.

Despite the disappointment of defeat, it was a much-improved performance from Kambosos Jr, who pushed Haney to the limit by pouring everything he had into the contest.

After an ill-fated dalliance with calling himself the Emperor, Ferocious Kambosos was back.

Unfortunately, it still was not enough.

"He's a great fighter," said Kambosos Jr, who recorded his second career defeat to move to 20-2.

Kambosos Jr came out all guns blazing in front of a parochial crowd at Rod Laver Arena.

Where in the first meeting he was tentative and reactionary, here he took the fight to his 23-year-old opponent, switching his stance from southpaw to orthodox early on in an attempt to upset the American's style and timing.

He had success too, always fighting on the front foot and never shying from the thunderous right hands coming his way to land some scoring shots on the American's body.

"He's a warrior, I take my hat off to George Kambosos," said Haney, who moved to a pro-record of 29-0.

Haney had success in the first fight with a dominant jab, but he adapted to the change in tempo with consummate ease, speaking volumes about the unbeaten American's talent.

After a fairly even opening four rounds, Haney gradually started to gain control of the fight with solid combinations, sitting down on his right hand off the back of his jab.

There were still moments when Kambosos hurt the American with body shots — and the crowd made their feelings known whenever he tied things up with a chorus of boos.

Kambosos Jr never stopped coming forward, but his bravery bordered on recklessness in the latter stages of the fight — particularly in the 10th — when Haney was landing rights at will flush on the chin of the challenger.

Still he came forward though, and even threatened to hurt Haney with a solid body shot in the 11th that had the champion wincing.

However, it was Kambosos who ended the fight bloodied around the eyes, unbowed by the encounter with his reputation further enhanced after such a gripping contest. 

"I feel that this was a much better fight than the first fight," Kambosos Jr said of his efforts, while acknowledging Haney's class.