Teddy Atlas says that Anthony Joshua didn't look interested in the fight vs. Andy Ruiz Jr. and gives credit to Ruiz for catching Joshua behind the ear, throwing off his equilibrium. (2:23)

NEW YORK -- It may not go down as an upset the magnitude of Buster Douglas knocking out Mike Tyson for the heavyweight world title, or even Hasim Rahman drilling Lennox Lewis to do the same, but Andy Ruiz Jr. knocked out Anthony Joshua in the seventh round to take his three heavyweight belts in an absolute shocker on Saturday night.

Sold-out Madison Square Garden was packed with 20,201, including many of Joshua's British countrymen who had made the trip expecting to see him smoke Ruiz, who closed as an 11-1 underdog, according to Caesars. But it became Joshua's Waterloo and crushed the chance of an undisputed championship fight between Joshua and Deontay Wilder that so many have wanted for so long.

"I just feel so good, man. This is what I have been dreaming about," Ruiz said. "This is what I have been working hard for. I can't believe I just made my dreams come true. I just want to thank my team and my family. The sky is the limit, baby."

Ruiz survived a knockdown in the third round and rallied to drop Joshua twice later in the round and then twice more in the seventh before stopping Joshua in a shocking scene.

Ruiz became the first fighter of Mexican descent to win a heavyweight world title and did so in the most dramatic fashion.

"That was my first time getting dropped on the floor. It just made me stronger," Ruiz said. "It just made me want it more. I just had to knock him down back. [I took his power] because of the Mexican warrior I am. I have that Mexican blood in me. Talking about the Mexican fighting style, I just proved it."

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A Mexican fighter had tried but failed to win a heavyweight title seven times before. That list included Ruiz, who lost an extremely close majority decision to Joseph Parker when they met for a vacant title on Parker's home turf in New Zealand in December 2016. Chris Arreola lost three tries, Eric Molina two and Manuel Ramos one. But now the flabby 6-foot-2, 268-pound Ruiz, who looks anything like a fighter and eats a Snickers bar before every fight, has a claim on boxing's biggest prize after he dethroned its biggest star this side of Canelo Alvarez.

"This is for all of Mexico. Mexico has its first heavyweight champion of the world, and we made history," Manny Robles, Ruiz's trainer, said.

The chiseled 6-6, 247-pound Joshua (22-1, 21 KOs), 29, was making his seventh title defense and his much-anticipated United States debut after regularly selling out stadiums in the United Kingdom. He came to these shores hoping to build his brand in America and because streaming service DAZN put up tens of millions of dollars to lure him here.

He was classy in defeat.

play 1:10 What's next for heavyweight champ Andy Ruiz Jr.? Teddy Atlas says promotor Al Haymon likely will keep the belts in the family, having his own fighter Andy Ruiz Jr. take on one of his other clients, like Deontay Wilder.

"Heavyweight boxing, baby. Thank you to the people who came out this evening. That's No. 1," Joshua said. "Heavyweight boxing is on fire. I just have to turn it around a few notches and bring it back my way. I don't want people to drown in their sorrows. This will show I have the power and the strength. It just wasn't my night. But listen, it is good for the TV. Good for DAZN and the people watching."

Joshua wasn't even supposed to face Ruiz (33-1, 22 KOs), 29, of Imperial, California. He was scheduled to fight undefeated New Yorker Jarrell "Big Baby" Miller, but Miller was bounced from the fight about a month ago after failing four voluntary Anti-Doping Association-administered random drug tests for three different banned substances -- GW1516, human growth hormone and EPO -- and being denied a boxing license by the New York State Athletic Commission.

After heavy hitter Luis "King Kong" Ortiz turned down the fight -- he will instead get a rematch this fall with Wilder -- Ruiz was the best available opponent who was willing, and anxious, to fight Joshua. So he took the fight fresh off a strong performance in a fifth-round knockout of Alexander Dimitrenko on April 20 and kept the momentum going.

Wilder shared his thoughts on Joshua's loss via social media.

He wasn't a true champion. His whole career was consisted of lies, contradictions and gifts.

Facts and now we know who was running from who!!!!#TilThisDay — Deontay Wilder (@BronzeBomber) June 2, 2019

Ruiz-Joshua began as a feeling-out process with almost nothing happening in the opening round other than Joshua landing a few jabs. A hard jab rocked Ruiz's head back at the start of the second round and Joshua continued to jam his jab at the much shorter Ruiz, who could not get past it.

But the fight changed dramatically in the third round, a clear candidate for round of the year. Joshua looked like he was going to end the fight when he blasted Ruiz with an uppercut and a left hook that dropped him hard. But Ruiz made it to his feet and went after Joshua and knocked him down twice in a wild round.

Ruiz nailed him with a right hand on top of the head, and Joshua's legs betrayed him before he went down. He got to his feet, but his legs were gone and he was wobbling all over the place as Ruiz went after him. He dropped Joshua for the second time under a hail of punches, and Joshua looked like he might not be able to recover.

What Are The Odds A look at some of the biggest upsets in boxing's heavyweight division over the past 45 years:

Saturday night

Andy Ruiz Jr. beat Anthony Joshua as an 11-1 underdog

2001

Hasim Rahman beat Lennox Lewis as a 20-1 underdog

1990

Buster Douglas beat Mike Tyson as a 41-1 underdog

1985

Michael Spinks defeated Larry Holmes as a 6-1 underdog

1978

Leon Spinks defeated Muhammad Ali as a 10-1 underdog

"As soon as Andy dropped him, he really slowed down," Robles said.

But by the start of the fourth round, Joshua seemed OK as he lashed Ruiz with a left hook that buckled him.

Ruiz landed a left hand early in the sixth round that buzzed Joshua, who backed up and looked to stay away. He flicked his jab hoping to keep Ruiz at bay, but Ruiz worked his way inside and fired a combination. And then another. And another.

"I could [sense he was hurt] but I just didn't want to throw away what I had. I just wanted to hunt him down even more and work the body," Ruiz said. "I just wanted to listen to the game plan."

In the seventh round, they were both in attack mode when Ruiz hurt Joshua and unloaded a dozen unanswered punches that finally dropped an exhausted Joshua.

He managed to beat the count, but Ruiz floored him again, sending him to one knee. He had his head down as he listened to referee Michael Griffin's count and barely beat it. He walked to the corner, where Griffin said something to him, but Joshua put his arms on the ropes with his back leaning on the corner post and Griffin waved off the fight at 1 minute, 27 seconds, leaving the crowd in shock.

"I want to fight. I don't do his job," Joshua said of Griffin. "I am never one of those fighters to disrespect a referee like he should have done this or he should have done that. He called it off when he thought I couldn't fight. It's a shame. But I don't want anyone to drown in their sorrows. It's the long game, not the short game."

Robles disagreed.

"He didn't want to continue," he said. "We had a great game plan -- to stay low, not fight tall and work behind the jab. Hit the chest, the body. I told him to either fight inside or stay outside. I did not want him to fight at midrange and put himself in front of the big punches."

Ruiz jumped up and down and celebrated wildly in the ring with Robles and the rest of their team after having authored one of the biggest upsets in recent boxing history.

According to CompuBox, Ruiz landed 56 of 206 punches (27 percent) and Joshua connected with 47 of 176 (27 percent).

At the time of the stoppage, Ruiz led 57-56 on two scorecards and Joshua was up 57-56 on the third card.

Joshua has the contractual right to a rematch and said he wants it.

Final punch stats Fighter Total Jabs Power Joshua 47 of 176 (27%) 24 of 104 (23%) 23 of 72 (32%) Ruiz 56 of 206 (27%) 17 of 87 (20%) 39 of 119 (33%) -- Courtesy of CompuBox

"One hundred percent. One hundred percent," he said.

Matchroom Boxing promoter Eddie Hearn, who promotes Joshua, said the rematch would be held in the U.K.

"AJ got sloppy. It was a beautiful combination in the third round," Hearn said. "He was in total control of the fight, but he got sloppy and never recovered. Listen, tonight was [Ruiz's] night, but AJ will come back 100 percent and we will make the rematch in the U.K. in November or December.

"But this night now belongs to Andy Ruiz. He made history in the heavyweight division. It will go down in history as a very big one. AJ has the heart of a lion and will come back stronger. Now at least we know the opponent for the end of the year in the U.K. Absolutely we will enact the immediate rematch. He will be devastated when it sinks in. It makes the fall fight a must win."

Ruiz said he is game for a second go with Joshua as much as he campaigned for the shot on Saturday after Miller fell out. But Ruiz had another plan before any of those rematch details are dealt with.

"Right now, I just want to celebrate," Ruiz said. "I just made history for Mexico. This is what I have been dreaming about since I was 6 years old."

And sometimes dreams do come true.