New Zealand heavyweight boxer Junior Fa has been stunned in his return to the ring, knocked out in the first round by 43-year-old Lucas Browne at Marvel Stadium in Australia.

Browne, who lost to Paul Gallen last year, was thought by many to be a spent force, and Fa was a heavy favourite to win his first fight since his defeat to Joseph Parker 16 months ago.

Bookmakers had Browne as big as a $14-1 underdog to beat Fa, but he made everyone look foolish – Fa most of all.

Fa barely got going, as Browne knocked him down early, with Fa looking shaky on his legs as Browne signalled for the referee to call the fight.

Fa was allowed back to his feet but Browne was hunting the KO and landed a thumping right hand over Fa's ear, leaving the 32-year-old on the canvas after just 118 seconds.

There was disbelief that the referee allowed Fa to continue after the original knockdown.

"Extraordinary scenes, I can't believe it. One right hand and it is over," said former Australian boxer Barry Michael, who had questioned whether Browne was too old.

"I didn't expect this, to be honest. Wow that was incredible."

"Are we still too old?" Browne asked, yelling out directly to Michael from the ring.

"He came and have a crack at me because I thought he should retire but he proved me wrong," Michael said.

"I just thought it was a deadset tough ask. But the last thing that goes with any boxer is his power and he's got power."

Fa now faces a tough ask to return to being a credible force in the boxing world, with his record now 19-2 and his reputation having taken a serious beating.

Two-time Kiwi Commonwealth Games gold medallist David Nyika had more success, claiming his third professional win with a unanimous decision victory over Karim Maatalla in a five-round fight.

Earlier in the card, Kiwi heavyweight Hemi Aiho moved to 19-0 after beating Christian Tsoye via TKO. Tsoye injured his elbow in the first round and could not continue.