NEW YORK — Anthony Joshua came down the aisle to the Madison Square Garden ring Saturday night as if he were going for a walk in the park.

It turned out to be like a walk in Central Park circa 1977, when it was at its most treacherous.

Joshua had come to New York to win over U.S. boxing fans the way he had mesmerized fight fans in the U.K, who turned out to see him in numbers unmatched since Jack Dempsey was fighting before crowds of more than 100,000 in the 1920s.

But Joshua wound up being just another foreign tourist mugged in New York City.

In a monumental upset second only, perhaps, in heavyweight title history to Buster Douglas’ KO of Mike Tyson, Joshua was knocked down four times and stopped in the seventh round by Andy Ruiz, a 20-1 underdog and one of the unlikeliest claimants to the heavyweight title in history.

And in the process, the previously unbeaten Joshua blew a prospective superfight with Deontay Wilder, his American counterpart.

“Things didn’t turn out the way we wanted them to,’’ boxing promoter Eddie Hearn of Matchroom Sport said. “Some fighters never come back the same. The future will show how Anthony Joshua responds.’’

Joshua’s immediate response was to skip the postfight news conference. No explanation was given for his absence.

Joshua, Wilder and Hearn weren’t the only losers of the night. Add Jarrell “Big Baby” Miller, Joshua’s original opponent, who was dropped from the card when he tested positive for performance-enhancing drugs; Luis Ortiz, the Cuban heavyweight who was offered $6 million to fill in for Miller but held out for $7 million, and Adam Kownacki, an unbeaten heavyweight from Brooklyn who apparently felt he just wasn’t ready.

All three must have been kicking themselves watching Ruiz kick the stuffing out of Joshua, who was widely considered one of the world’s two best heavyweights.

“I’m still pinching myself to see if this is real, man,’’ Ruiz (33-1, 22 KOs) said. “Amazing.’’

Joshua will undoubtedly invoke the rematch clause to try to reverse the result of the Ruiz fight, but there is no way to undo the damage to his reputation. As the two came together before the opening bell, the size difference and disparity in physical conditioning was almost comical, like a movie fight between Dwayne “The Rock” Johnson and Lou Costello.

Before the fight, Ruiz embraced his image as a jolly fat man, even lobbying for an endorsement deal from Snickers. “I even actually gained 5 more pounds than I normally carry, because Anthony’s a big guy,’’ he said.

But in the ring, Ruiz was more tiger than elephant, undressing Joshua in front of a highly partisan sellout crowd of about 20,000, many of whom had made the trip over from England. They had spent much of the night chanting Joshua’s name, singing British pub favorites, and booing the image of Ruiz in his dressing room whenever it appeared on the overhead screens.

By the time it was over, at 1:26 of the seventh round, that same throng was booing the man they had come to celebrate.

At 5-foot-11 and 268 pounds, Ruiz was 7 inches shorter and 20 pounds heavier than the chiseled Joshua. But in the same city where another unlikely title challenger, “Two-Ton” Tony Galento, dropped the legendary, and heavily favored, Joe Louis 80 years ago this month, Roly-poly Ruiz went Two-Ton Tony three knockdowns better.

Even more impressively, Ruiz did all his damage after having been floored by a picture-perfect left hook early in the third round, something that had never happened to him in his previous 33 fights.

“That was something, wasn’t it?,’’ Ruiz said. “I was like, ‘What the hell just happened?’ I knew I had to pay him back.’’

Up at the count of five, Ruiz began crowding Joshua and flurrying with speedy but wide punches. One of them caught Joshua high on the head and wobbled him. Sensing blood in the water, Ruiz landed several more nondescript shots — none of his punches were particularly clean or memorable — and Joshua hit the deck.

He was up at the count of six, but one of the concerns about him, his suspect chin, was on full view as Ruiz flailed away for the remainder of the round. With less than 10 second to go, Joshua was down again, referee Mike Griffin continuing the count after the bell. Joshua was clearly hurt but allowed to return to his corner, and the fight continued.

A puzzlingly action-free fourth round followed in which Ruiz seemed to let Joshua off the hook. Joshua won the fifth with his jab but showed signs of tiring in the sixth. But in the seventh, Ruiz began banging Joshua to his seemingly firm midsection and the punches clearly had an effect. Soon after, Joshua was down again, from a right to the jaw — Ruiz’s most technically proficient punch of the fight — and a few seconds later, down to a knee for the fourth knockdown from a sloppy flurry of punches to the head.

When Joshua arose, he leaned against the ropes as Griffin asked if he wanted to continue. Joshua made no reply, nor did his body language indicate he had any inclination to continue. Given no other choice, Griffin waved the fight off as Joshua, a sick smile on his face, spread his arms in either disbelief or resignation.

“I think he probably could have continued,’’ Ruiz said, “But I just would have stopped him anyway.’’

At the time of the stoppage, Ruiz led on two cards, 57-56. Joshua led by the same margin on the third. “I knew I didn’t want to let this fight go to the judges,’’ Ruiz said.

It was Joshua’s fourth fight since he burst onto the scene in April 2017 with an impressive 11th-round TKO of defending champion Wladimir Klitschko before 90,000 fans at Wembley Stadium, a fight in which Joshua overcame a sixth-round knockdown to outlast his 40-year-old opponent. Joshua had been decidedly less spectacular in his ensuing three fights — a 10th-round TKO of Carlos Takam in October 2017, a unanimous decision over Joseph Parker in March 2018, and a seventh-round TKO of Alexander Povetkin in his most recent fight last September.

But few people other than Ruiz believed he could be upset in his long-awaited U.S. debut. “I wanted to show all the doubters that I belonged here,’’ Ruiz said.

In addition to that, Ruiz, a 29-year-old father of four, became the first fighter of Mexican heritage to win the heavyweight title, an honor he was especially proud of.

“We just made history, baby,’’ he said. “Our lives are going to change. Ain’t going to struggle no more.’’

More from Yahoo Sports:

• World No. 1 Naomi Osaka joins list of French Open upsets

• Cubs troll Cardinals fans by ‘booing’ Kris Bryant

• What SEC lifting alcohol ban at stadiums means

• Three pressing questions Warriors must answer in Game 2