NEW YORK >> Conor McGregor lay waste to a battered Eddie Alvarez and brazenly demanded his second UFC championship belt.

“Where’s that second belt,” McGregor bellowed to a roaring crowd.

McGregor snatched his new lightweight championship belt, paired it with his featherweight title, and UFC’s first two-class champion in the promotion’s history plopped himself on top of the cage and absorbed the scene of his historic night.

“I’ve spent a lot of time slaying everybody in the company,” McGregor said.

Alvarez is the latest victim on the list.

McGregor knocked out Alvarez in the second round to win the UFC lightweight title Saturday night, becoming a dual title holder. He dominated from the opening bell of the main event of UFC 205 at Madison Square Garden and the sold-out crowd of 20,427 loaded with A-listers went wild with each blow.

McGregor, also UFC’s featherweight champ following a 13-second knockout of Jose Aldo, had predicted a fourth-round KO.

Unlike UFC’s laborious battle to reach New York, McGregor wouldn’t make anyone wait.

UFC has not decided if McGregor (21-3) 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 (28-5). McGregor was the clear aggressor from the start, dropping 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.

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.

“Eddie is a warrior but he shouldn’t be in there with me,” he said. “I’m at a different level. Now, I celebrate as champion of two divisions.”

UFC was live and legal in New York for the first time since an MMA ban was lifted earlier this year.

To celebrate, UFC stacked the card with three title fights that set a promotion and MSG gate record with $17.7 million. The 1999 boxing match between Lennox Lewis and Evander Holyfield drew a record $13.5 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.

The two-decade ban imposed by New York left only unsanctioned MMA fights in the state. State lawmakers and Gov. Andrew Cuomo agreed in April to end the ban following years of failed efforts by supporters. The law authorizing the sport took effect in September and UFC optimistically already had MSG booked.

New York couldn’t wait one more night.

McGregor, as he had been all week in New York, was the star of the show — even with Madonna and Hugh Jackman in the arena. McGregor’s fans wore Irish flag capes and his fellow countrymen sang “Ole Ole Ole” in the concourse and stands throughout the show.

UFC last ran a major show in the state at UFC 7: The Brawl in Buffalo on April 7, 1995. UFC, under Lorenzo and Frank Fertitta, exploded into a global phenomenon, become a staple on network television and ran PPV cards that hit 1 million buys during the ban. UFC 205 was expected to reach around 1.5 million PPV buys. UFC sold for approximately $4 billion to a group led by Hollywood entertainment conglomerate WME-IMG in July.

Tickets at face value and on StubHub only seemed to be selling for that much apiece.

The fans got plenty of bang — and kicks, punches and elbows — for their buck.

Yoel Romero caught Chris Weidman with a flying right knee and finished him off in the third round with a spectacular, bloody knockout. Weidman sat loopy in the octagon as blood poured down his face and onto his chest. Romero sprinted toward the cage, flipped over the top and ran a lap in celebration.

Romero’s win made him the No. 1 contender for Michael Bisping’s middleweight title and they wasted no time hyping that potential matchup. Bisping was shown on the big screen and extended his middle fingers at Romero.

“It is an honor to be a part of UFC 205 in Madison Square Garden but now I want my shot at the title,” Romero said.

Miesha Tate is out of title shots.

Tate, who played a pivotal role in the women’s division rising to prominence in UFC, announced her retirement inside the octagon following a loss to Raquel Pennington. The 30-year-old Tate says the loss played a role in her decision.

“I had a lot more to give but I couldn’t pull it out of myself,” she said.

Tate defeated Holly Holm in March to win the bantamweight title and then lost the belt in her first title defense to Amanda Nunes in July.

Tate (18-7) had coached Pennington on “The Ultimate Fighter,” a reality show used by the UFC to recruit new talent.

The Madison Square Garden crowd gave Tate a loud ovation following her surprise announcement.