Joshua was an overwhelming favourite to keep hold of his three recognised world heavyweight titles on his stateside debut at Madison Square Garden.
Yet it quickly became evident that Ruiz was not reading from the same script when, after being floored himself in the third round, the Mexican rose from the canvas to put AJ down twice and set the wheels in motion for one of the greatest upsets in boxing history.
Joshua never truly recovered from such a calamitous round, with referee Mike Griffin waving the contest off in the seventh to crown Ruiz as the new, and unexpected, heavyweight champion of the world.
As he was introduced by MC Michael Buffer, the Brit did not seem his typical confident self as he laid back on the ropes, chewing his mouthguard excessively and having his neck massaged by a member of his entourage.
He did not appear primed for his American bow.
Rumours began to circulate of Joshua being given a pasting in sparring before the fight, which could explain his sheepish body language and guileless performance.
But Haye has shed light on a conversation with Carlos Takam – the French heavyweight beaten in a close encounter with Joshua in 2017 – who told him the 29-year-old isn’t challenged well enough in sparring.
“[Joshua is] a supreme athlete, he’s probably physically superior to every other heavyweight on the planet,” Haye said.
“But his boxing experience is quite limited compared to Andy Ruiz, and you can’t make up 10 years of extra boxing experience with a training camp – no matter who your coach is.
“It’s all about being in the ring with guys in sparring. I talked to Carlos as well and he said a lot of the sparring AJ does is technical sparring. It’s not full on.
“It’s not like the sparring I did, it’s not like the sparring Derek [Chisora] does. We fight. We’re just not getting paid for it.
“You just get fight hardened. Every round is tough. I did loads of rounds with Carlos, rounds that I lost, and they were hard rounds. I’m like ‘guys, this is not nice. I’m not enjoying this. This is really, really bad. I really need to fix up.’
“So I’d come back the next day, try again, same thing happens, so I’m losing rounds.
“But that’s what you need, you need that. How many rounds does Joshua do where he loses? In sparring, I don’t know. I don’t imagine that many.
“Maybe he needs rounds that he loses in sparring. For that, you need to pay sparring partners.
“I had Deontay Wilder in sparring, Mariusz Wach. Two rounds in, two rounds in so it’s horrible, so I’m struggling. So come fight night, it feels a lot easier.
“I’m not sure if he’s doing that. Maybe he is, maybe he isn’t.
“But it didn’t look like it on the night and maybe he needs to incorporate some of that hard, tough sparring behind close doors, with bigger gloves and head guards so he doesn’t get cut or damaged.”