Andy Ruiz Jr. stunned British boxer Anthony Joshua with a seventh-round technical knockout Saturday night to become the first fighter of Mexican descent to claim the heavyweight title.

The 29-year-old native Californian shocked a sellout crowd at Madison Square Garden with his surprise victory, marking one of boxing’s biggest upsets behind Buster Douglas’ win over Mike Tyson for the heavyweight title in 1990.

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"I just feel so good, man," Ruiz said. "This is what I've been dreaming about, this is what I've been working hard for. I can't believe I just made my dreams come true."

The 270-pound heavyweight knocked down Joshua twice in the third round and did it two more times in the seventh before referee Mike Griffin ended the fight at 1:27 in the round. The 247-pound Joshua was unsteady and seemed to stumble toward the wrong corner after the final blow.

"Sorry I let my fans down, sorry I let my supporters down," Joshua said.

Joshua (22-1, 22 KOs) and Ruiz were both knocked down in an electrifying third round that had the crowd howling with each heavy hit. The 29-year-old Joshua never seemed to fully recover from the knockdowns.

Ruiz (33-1, 21 KOs) accepted the unexpected title shot against Joshua with just six weeks to prepare after several failed drug tests moved the British champion’s original opponent, Jarrell Miller, to the sidelines.

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The underdog went on to make boxing history and win the WBA/IBF/WBO/IBO championships.

"My life is going to change," Ruiz said. "I don't have to show them no more."

The Associated Press contributed to this report.