Gallen vowed to give the game fight away if he lost to Hopoate in their charity bout in Sydney on Friday, but will punch on after flattening the 45-year-old with a second round knockout.

Hopoate had pledged to "retire Gal from boxing and the NRL" during the pre-match banter but soon had to weigh up his own future inside a packed Horden Pavilion.

"I got caught by a good punch and I can't hide from that, I went to sleep and fell over," he admitted.

Gallen dominated from the opening bell, with a succession of jabs setting the tone for a one-sided heavyweight contest.

Hopoate, in the ring for the first time in nine years, sought to grapple and frustrate Gallen, but when the Sharks veteran found openings he sensed blood.

Gallen had Hopoate on the ropes, and in strife, late in the opening round and although the bell prevented further punishment it was only a short reprieve.

Hopoate headed to the canvas early in the second, the stoppage coming quicker than Gallen anticipated.

"I didn't think it would finish so early, he's a tough guy when we've sparred before," Gallen said.

"I could feel Hoppa's power but I just kept jabbing him to his body and I knew that was slowing him down.

"When I knew I had him gone I half looked at the ref to stop it.

"The last couple of weeks have got personal but I'm happy to shake hands with him and make up.

"I feel like I'm getting better, but I'm looking forward to getting back to footy."

Australian Associated Press