But it led to the opening he needed and Berridge caught Riva flush with a left hand and the stunned South American was unable to answer the 10 count.
Berridge's first destination was the corner where his originally scheduled opponent, Adrian Taihia, was sitting.
Things got even more personal as Taihia, the 31-year-old NZPBA super middleweight title holder, entered the ring during Berridge's television interview for a war of words the fighters kept separated by their entourages.
The bad blood between the pair goes back months when Taihia (9-1) accused Berridge (21-1-1) of "running his mouth" about a lack of willing opponents in New Zealand, claiming he had agreed to face him until Berridge's new promoters Duco Events kept changing the money offer and number of rounds for the fight.
Berridge's cousin and Wanganui trainer, Paul Berridge, said the men were finally linked to battle on Thursday night before Taihia withdrew, citing a broken nose in training.
"He pulled out of the fight, Duco Events put the Argentine in front of Rob. I just think he's trying to play some mental game with Rob."
Paul Berridge said Taihia had been "barking" from the corner during the fight, trying to distract "The Butcher", which is what prompted his cousin to respond after the final bell.
"He said, 'that's what you expect', you know, 'if you fight me'.
"Hats off to the way Rob dealt with it when he came in the ring.
"Rob's always class but he's more of a class act than that."
Berridge said in the interview he was looking to get another fight this year, the logical place being the rescheduled David Tua comeback against Alexander Ustinov on November 16. "I think they're looking at Daniel MacKinnon on that Tua card, but that's not confirmed," said Paul Berridge.
The other option would be to arrange the bout with Taihia, although he is listed online as having a match against Timo Masua at Auckland's ABA Stadium on November 30.
Paul Berridge said given the current hype the match might still happen and his cousin would be looking for a quick knockout because of Taihia's trash talk and the way he challenged him. "To do that on that fight and bring it to New Zealand's attention, [Taihia's] going to look silly if he doesn't live up to his word."