Conor McGregor knocked out Eddie Alvarez in the second round to win the UFC lightweight title and become the first two-class champion in the promotion's history.
McGregor dominated from the opening bell of the main event of UFC 205 at Madison Square Garden on Saturday night and the sold-out crowd roaring with each blow. McGregor is now the reigning featherweight and lightweight champ.
UFC has not decided if McGregor will be allowed to defend both championships. UFC President Dana White said McGregor could be about the only fighter in the promotion to handle that kind of fight load.
McGregor crouched inside the cage waiting for the bell to ring and attack Alvarez.
McGregor was the clear aggressor from the start and dropped Alvarez three times in the first round. Alvarez, out of Philadelphia, bounced up the first two times and took a severe beating on the third. McGregor forced Alvarez to fight with his back to the cage and dominated the rest of the round.
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McGregor placed his hands behind his back in the second, taunting and toying Alvarez to hit him. McGregor, UFC's biggest box office star, unloaded a left and ended the fight.
He demanded both belts and slapped them over his shoulder before he sat on top of the cage.
"I've spent a lot of time slaying everybody in the country," McGregor said. "I'd like to take the chance to apologise to absolutely nobody."
UFC was live and legal in New York for the first time since an MMA ban was lifted earlier this year.
UFC stacked the card with three title fights that were expected to help set a gate record of more than $A22 million at MSG. The 1999 boxing match between Lennox Lewis and Evander Holyfield drew a record $A18 million.
Tyron Woodley defeated Stephen Thompson via majority draw to retain his welterweight title in a fantastic fight and Joanna Jedrzejczyk successfully defended her UFC women's strawweight championship with a unanimous decision win over Karolina Kowalkiewicz.
But the night belonged to McGregor.
"What's next for me?" McGregor asked inside the cage.
The easy answer: Whatever the Irishman wants.
