Anthony Joshua never imagined his US debut at Madison Square Garden on 1 June would be like this: defending his four world heavyweight titles against the long-shot Andy Ruiz Jr, who has landed boxing’s equivalent of the lottery.

Picked from a short and meagre list of candidates to fight the unbeaten champion at the revered New York venue, the Mexican-American with a respectable but underwhelming CV was confirmed on Wednesday as the late replacement for perhaps the dumbest challenger in recent times, the serial dope offender Jarrell Miller.

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Miller – even with hometown pulling power – was hardly a limelight choice in the first place and once he has served his laughably inadequate six-month ban for failing three drug tests, he will be shuffled back in the pack.

Ruiz, meanwhile, has already begun to shout loudly about his chances – and who could blame him? As Adam Smith, head of Sky Sports Boxing, said: “Ruiz has snatched the golden ticket.”

A glance at the resume of Ruiz over a decade as a professional reveals a string of wins against second-tier heavyweights in small venues from Tijuana to Tucson, before stepping it up in recent years. Since losing in his previous world title bid, a majority points loss to the then WBO champion Joseph Parker in Auckland two years ago, Ruiz has fought three times. He stopped the weak-chinned Devin Vargas in a round, edged everybody’s favourite trial-horse, the 39-year-old Kevin Johnson, and forced the 36-year-old Alexander Dimitrenko, who once was a contender, to quit after five rounds only 11days ago in California.

Ruiz has lost only once in 33 bouts but,at 6ft 2in and 18st 7lb, he will be looking up at 6ft 6in Joshua – and, more than likely, the referee after maybe six or seven rounds.

Ruiz will give it a good shot. “I think the fight is going toe-to-toe, two guys smashing each other’s faces,” he said. “I’m going in there to throw combinations like I’ve never done before, to improve my speed.

“A lot of people underestimated me, and I’m used to that. My whole life people underrated me. I’m not going in there scared and I’m not going in there nervous. I’m going to go in there mad and to take what’s mine.

“Being so tall, he fights like a big robot. With my style, my speed, my movement, I don’t think he’s fought anybody like me. I don’t think he’s good going back. When I do pull out this win, everything is going to change. I’m going to bring the titles back to Mexico. It’s a win-win situation, but the main thing is to win the fight and make history.”

He will make money – probably more than $7m, the purse the veteran Cuban Luis Ortiz mysteriously turned down. Making history might have to wait.

This is a banana-skin fight for Joshua. All his belts – representing the IBF, WBA, WBO and IBO – are on the line for just the second time in his eighth world title fight, which might be his main motivation on an otherwise low-key evening. He has not fought since September, when he knocked out the formidable Russian Alexander Povetkin in front of 80,000 fans at Wembley Stadium – in the same ring where he brought Wladimir Klitschko’s long career to an end two years ago.

Since beating Klitschko, Joshua has been trying to emulate the Ukrainian by unifying the title, but efforts to fight either the WBC title-holder, Deontay Wilder, or the linear champion, Tyson Fury, have ended in predictable frustration because of the sport’s tangled politics.

Joshua said before a workout in Sheffield on Wednesday:“Ruiz is a different kind of challenge but one I embrace. We have worked in the gym week on week. The rent will be collected.”

He also argued for more stringent regulations to be put in place when fighters fail doping tests in the wake of Miller’s meagre six-month ban.

“Maybe there needs to be more of a situation where it’s not just a random six-month ban. I know, for instance, if I carry a bladed article I’m going to get ‘X’ amount of time in jail, if I carry a weapon of destruction I’m going to get a certain amount of time in jail, so you know [the consequences of what will happen].

“Six months is news to me, it’s like: ‘Why did he only get six months?’ It should be ‘Miller’s definitely getting this’ – that’s my opinion on it.”