Furious all week about Browne dismissing him as a "footballer", the retired rugby league great sent 'Big Daddy' to the canvas twice inside the first two minutes with a series of devastating blows to the head.

Browne was given a standing count on the first occasion but was unable to continue after being laid out a second time.

"I don't know why, but I woke up this morning and I didn't say it to anyone but I knew within myself I'm going to win in the first round. I'm going to knock him out in the first round," Gallen said.

"I kept saying to myself I'm going to knock him out in the first round - and it happened."

Once again, Gallen entered the ring as the underdog with Browne insisting he'd be the one to land the knockout blow.

But, urged on by his 2016 premiership-winning teammate Andrew Fifita and several other Sharks in the near-sellout crowd, it was Gallen who lived up to his own pre-fight promise to destroy Browne's career.

"I had confidence in my chin against a guy like this," Gallen said.

"The more I train and the more I spar in the sport of boxing (the better I get."

Gallen ranked his win among the highlights of his career.

"Nothing will replace the premiership that I won with the Sharkies," he said.

"I'm a prize fighter, I'm not here for titles. I'm about taking fights that people want to see," he said.

"I'll be having as many fights as I can so I can cash in."

Now undefeated in a dozen bouts, Gallen collected almost half a million dollars for his latest victory, which has likely set up another monster pay day later in the year against budding Olympian Justin Huni.

Browne is scheduled to meet Huni before the latter heads to the Tokyo Olympics as an amateur but that blockbuster could be in doubt after Wednesday night's showing from the 42-year-old.

There may not have been any belts on the line - mostly pride and money - but the fight still drew a galaxy of stars as well as Sharks players.

Australian boxing's new main man Tim Tszyu was a conspicuous ringside observer, while a host of St George Illawarra players including another of Gallen's title-winning teammate from 2016, Jack Bird, along with Tariq Sims and Corey Norman, were also on hand.

Even Trent Merrin joined his Dragons teammates at the fight just hours after announcing his retirement.

They weren't disappointed as Gallen, against all odds, continued his rapid rise up the boxing ranks.

Browne insisted this was not the end for him.

But the veteran conceded he copped a hiding.

"I don't know where exactly I got hit the first sort of shot, but basically I can't hear out in my left ear.

"It just took the equilibrium off me and I couldn't recover."

Australian Associated Press