Eddie Hearn dropped Matchroom CEO Frank Smith during a comical sparring session held between the promotional kingpins.
Hearn, whose promotional stable includes former heavyweight world champion Anthony Joshua and current pound-for-pound king Canelo Alvarez.
He had a brief amateur career but has ruled out the possibility of returning to the ring for a white-collar fight.
But he and Smith, Hearn's right-hand man, took to the squared circle in San Diego as they launched Alvarez's forthcoming clash with Dmitry Bivol.
The promoter immediately held the advantage with his height and the pair clinched, before Smith tried to let his hands go after the break.
Hearn then leaned on his opponent on the ropes as he tried to use his size to the audience's pleasure as they burst into laughter.
The 42-year-old began barreling in some huge body shots on the ropes which caused Smith to bounce away and look for an escape.
Hearn continued to have the upper hand over Smith before Hearn shouted "not again" after being caught low in the stomach.
However shortly afterwards Hearn made his breakthrough dropping Smith with a well-timed left hook to the body which saw Smith double over in pain.
The pair took their final exchanges to a warm applause from the small crowd in America as the pair embraced and looked exhausted.
Smith joked at the end: "Do you want to do another fight? Easy light work."
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Hearn has been in boxing for several years and was largely responsible for its re-emergence to the mainstream with Sky Sports.
They have staged huge events including fights such as Anthony Joshua's win over Wladimir Klitschko and Carl Froch's famous rematch with George Groves.
However he has admitted that he is looking to retire from promoting in the sport at around 50-years-old.
“When I get to 50, maybe even before, I’m f***ing off. You’ll never see me again. I’m gonna go and sit on a beach,” Hearn told reporters in America.
“I have a huge amount of respect for Bob Arum because [he’s doing this and] he’s 90 years old. I’ll put this on record now, if I’m sitting here at 60, shoot me now.
“I’m out at 50. This is a terrible business to be in. Sleepless nights, up on different time zones, arguments, people trying to f*** you.”
