"I haven't been in the ring for half a year but man, what a hard head," Parker said of his 39-year-old opponent. "He's durable and he had a lot of heart and didn't want to stop, but I guess he took a lot of punishment.
"The ref did his job. It was the right call. I thought I was going to have to keep beating him to the end… the ref did the right job but man he's got a hard head.
"I landed some flush shots and he wobbled a lot of times but he kept coming forward."
There was a nice moment shortly after the fight when Leapai entered Parker's room and the two Samoans shared a hug, with Leapai telling him he had a huge future before offering his services as a sparring partner.
Sporting a goatee beard and the trimmest physique of his professional career, Parker, 27, looked a class above his fellow Samoan, even if Leapai's haymakers posed an intermittent threat.
It improves the South Auckland heavyweight's record to 26-2, with 20 knock outs. He remains undefeated against anybody outside the UK.
If Parker was looking to make a statement in his Matchroom debut, in a fight that was co-main event to Demetrius Andrade's defence of his WBO middleweight belt against Maciej Sulecki, it was mission kind of accomplished.
Sure, the early knockout that looked inevitable never materialised but owed more to the cement-like quality of Leapai's head than a lack of shots from Parker.
"I wasn't so much frustrated but I think maybe I was just rushing. I've got fast hands so sometimes I rush a lot of the punches out. When I went to the corner they said slow it down, and then I have to pick my shots."
It didn't look as if the fight would go beyond the first as Parker poured it on. Leapai weathered that but it was obvious his hopes rested somewhere between slim and no.
Leapai took a breather in the second and third rounds for apparent low blows – Gonzalez never appeared overly concerned – but he couldn't stop the barrage of upper cuts and right hands he was wearing.
Parker's energy flattened out slightly by the sixth round although he never looked anything other than in complete control.
It was his first fight in the US since his TKO of Keith Thompson in 2014, 19 prize fights ago. In front of a large and boisterous Rhode Island crowd unafraid of voicing "you suck" hot takes on the fighters, Parker kept them interested if not 100 per cent invested.
Parker went into the fight at 109kg, with Las Vegas-based trainer Barry saying it was the most finely tuned he had seen his charge. He had looked sharp in training all week and, to the surprise of nobody who has had anything to do with Parker, relaxed on the day of the fight.
"He was in great shape," Barry said. "Hey, it would have been nice to knock him out but the flip side is we got some excellent rounds and Joe put his skills on for a lot of people to see.
"The speed and the combinations he threw were most impressive. He threw some huge punches that landed and Alex came out in the second round and he did it again and I sort of said, 'This is a tough old guy and we're going to have to break him down."
"I could not believe the punches he took and I was a little surprised the fight wasn't stopped a lot earlier. Honest to god, I don't know the power punch stats but there were a lot of power punches in this fight."
Leapai came into the fight at short notice, having replaced American Eric Molina who proved too hard to tie down to a workable contract. Leapai had been in camp with trainer Noel Thornberry, but not working at the intensity needed to face a fighter of Parker's class.
The fight is in the books, but in all reality there was little to gain for Parker aside from another notch on his belt.
It is expected Matchroom promoter Eddie Hearn will arrange a fight against Brit Dereck Chisora, possibly as early as September, which will be a significant step up in quality and expectation.
"Whoever's ready to jump in the ring; I'll fight anyone," Parker said. "I don't care who, I'll take care of business."
If that goes to plan, Parker could be fighting somebody as accomplished as Alexander Povetkin by year's end.
That will be mark the end of his current deal with Matchroom, but the expectation from both parties is that will be extended as there is a lot of optimism around the camp despite the 2018 setbacks.
Parker is still ranked high on most rankings lists and importantly, he is at least two years younger than those ranked ahead of him.
Most intriguingly, he remains the only fighter to have beaten current champion Andy Ruiz, having prevailed in a close decision in Auckland in 2016.
Indisputably, Parker's career hit a sizable speed bump in 2018. This was a victory that was expected and was duly delivered, nevertheless, it points to a boxer veering back into the fast lane.
Dylan Cleaver travelled to the US courtesy of Duco
