Jim Kambosos, father and manager of former world champion George Kambosos, felt his son did not apply enough pressure on Devin Haney in their lightweight title fight.

Before a crowd of over 40,000 at Marvel Stadium in Melbourne, Haney outboxed Kambosos over twelve rounds to secure a unanimous decision.

All three of the official judges had Haney ahead by at least eight rounds, with tallies of 118-110, 116-112 and 116-112.

The victory made Haney the undisputed world champion at 135-pounds by uniting the WBO, WBC, IBF and WBA world titles.

It was the first bout for Kambosos since becoming a world champion with his tremendous upset over Teofimo Lopez from last year.

Haney, who had a four-inch reach advantage, began pumping a steady jab from the very start of the fight and continued to use that punch as the main weapon until the final bell.

Kambosos was too relaxed in the fight, claims his father, which allowed Haney to control the fight with his boxing ability.

“[George] had to put more pressure [on Haney]. He let him become too comfortable. If you’re going to be too comfortable with that jab, you’re not going to get inside. George has to start fast and make Devin uncomfortable from the get-go," Jim Kambosos said.

“George started to roll in the seventh round... he started to land but he was playing catch-up.”

There is an immediate rematch clause, with Kambosos almost sure to exercise that option. Like the first encounter, the second fight will take place on Australian soil.

Haney entered the fight with impressive back to back wins over former world champions Jorge Linares and Joseph Diaz.