The Mexican-American giant-killer, who cut his teeth fighting bigger opponents, says the Briton’s style is perfect for him

The superficial differences in the physiques of Andy Ruiz Jr and Anthony Joshua were laid bare even more dramatically than six months ago at Friday’s weigh-in on a sun-splashed afternoon outside the Al Faisaliyah Centre in downtown Riyadh.

The doughy Ruiz came in at 20st 3lb (283lb) for Saturday’s rematch, more than a stone above the svelte-for-him 268lb of their encounter in June, while the slimmed-down yet still-sculpted Joshua weighed 16st 3lb (237lb), down 10 pounds from the worst night of his boxing life.

Yet the physical disadvantages Ruiz will face at the Diriyah Arena on the north-west outskirts of the Saudi capital – four inches in height, eight inches in reach with a body mass index breaking the scale – are hardly different than those he overcame the first time when he overwhelmed Joshua for the WBA, IBF and WBO heavyweight titles at Madison Square Garden.

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That was no fluke. No “punch from the gods” that can be explained away. After showing otherworldly punch resistance after coming back from a heavy knockdown in the third round, Ruiz’s deceptively quick hand speed and in-fighting made the upright champion look basic – and offered a compelling case for why the Mexican-American nicknamed the Destroyer appears to be a stylistic nightmare for a tall-and-straight puncher such as Joshua.

Play Video 1:23 Anthony Joshua and Andy Ruiz Jr weigh-in before Saudi showdown – video

“I think his style was just perfect for me and I think [Saturday] will be the same,” Ruiz said this week. “I think he will box around nicely for four or five rounds until I take the pressure to him, start hitting his body and mixing it up.

“That is exactly what we have been training on. Being small, being more slick, applying pressure, throwing combinations and being first to the punch. I know he is going to try to box me around, that is why he lost some weight, he will try to keep me away with the jab. But that’s what we have been practising for.”

The initial efforts to make sense of Ruiz’s shock upset – a stunner that ranks alongside Buster Douglas v Mike Tyson and James Braddock v Max Baer among the most seismic in the division’s lengthy annals – pointed toward the superior amateur pedigree of the 30-year-old from south-eastern California, who banked nearly three times as many fights and a decade more experience in the unpaid ranks as the late-starting Joshua.

Yet a closer inspection of these formative years offers further insight into Ruiz’s giant-killing ways: he has been cutting his teeth on bigger guys nearly his entire life.

Ruiz was 12st 8lb (180lb) at nine years old, which led his father to put him in with older kids who could handle the youngster’s unique blend of size and speed. He was made to spar with professionals often twice his age on those endless trips across the US-Mexico border to train at gyms in Mexicali, where he became accustomed to problem-solving against opponents far bigger than him.

Facebook Twitter Pinterest Andy Ruiz Jr Anthony Joshua at the weight in in Riyadh. Photograph: Valery Sharifulin/Tass

Andy Ruiz Sr recalls the way he got the attention of Freddie Roach when he first made the 200-mile journey from Imperial to Los Angeles to train for the Mexican Olympic trials at the Wild Card boxing club, getting the best of a series of the famed trainer’s professional heavyweights when he was still a teenager.

“He beat the shit out of Javier Mota, a much taller Mexican, who had 24 fights and one loss at the time,” the elder Ruiz said. “He knocked that guy down when he was 16 years old.”

Jorge Muñoz, who runs the Sparta boxing gym in El Centro where Ruiz came of age and still occasionally trains, believes the seeds planted during those Wild Card sessions more than a decade ago came into full bloom when their hometown hero got the chance of a lifetime against Joshua. “You could see all the stuff they taught him to fight the big guys, all those tricks about putting the forehand on their neck, hitting them in the forehead.” Muñoz said. “Those little details work for him because he’s always been in with guys who are taller. He knows how to work inside and over [in Europe] they don’t know how to work inside.”

Muñoz added: “It’s the Mexican style: body shots and uppercuts. Andy has a crazy jab to the stomach and Joshua is not used to getting hit right there. If you watch all his fights, nobody ever hits him there, because he’s fought all those guys from over there who are just one-two, one-two [to the head] and nothing with the body.”

Joshua will attempt to become only the fourth deposed heavyweight champion to win an immediate rematch after Floyd Patterson (against Ingemar Johansson in 1960), Muhammad Ali (against Leon Spinks in 1978) and Lennox Lewis (against Hasim Rahman in 2001).

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A greater number have failed in the task, among them Jersey Joe Walcott (both to Rocky Marciano), Patterson (both to Sonny Liston), Larry Holmes (both to Michael Spinks) and Mike Tyson (both to Evander Holyfield).

Muñoz believes six months is too quick a turnaround for Joshua to absorb the necessary lessons.

“I think it’s too short notice,” he said. “Joshua already knows how he could beat him, by jabbing and moving around, but Andy already knows what he needs to do. When Joshua won the gold medal, he fought from the outside. But that’s all amateur. Eventually a pro gets in there and it’s about how you work on the inside.”

Ruiz’s father, who says he won $50,000 betting on his son to defeat Joshua when they first met, said he is even more confident for Saturday’s showdown – even if it looks as if he has enjoyed a few too many cheat days at hometown favourites Johnny’s Burritos and Donut Avenue. “We’re going to win the fight.”