NEW YORK - Eddie Alvarez, his mouth bloodied from Conor McGregor's strikes, looked to be in a bit of disbelief as the referee came to his aid on Saturday night. The greatest night of the Philadelphia fighter's career was over. And it ended with a one-sided loss.

McGregor knocked out Alvarez in the second round at Madison Square Garden in UFC 205 to take Alvarez's UFC lightweight title. McGregor is the first UFC fighter to hold titles at two weight classes at the same time, as he entered the fight as the company's featherweight champion.

Alvarez stressed in the pre-fight build-up that McGregor was an inflated champion who had climbed the UFC ladder without facing a real test. The Kensington native and North Catholic graduate said he would be the stiffest challenge of the Irishman's career.

McGregor passed that test with flying colors.

"Eddie is a warrior, but he shouldn't be in there with me," McGregor said. "I am a different level. Now, I celebrate as champion of two divisions."

McGregor looked stronger, bigger, and quicker than Alvarez. He threw his left hand with ease and baited Alvarez to trade punches instead of takedowns. The final blow was a vicious left-right-left combination that dropped Alvarez to the mat. McGregor positioned himself on top and fired off a few more rounds before the referee stopped the bout.

"They're not on my level," McGregor said. "You have to have size, reach, some attributes. If you come in any way equal to me, I'm going to rip your whole head off. I tell you that every time."

McGregor dropped Alvarez three times in the first round. Alvarez escaped a ground grapple near the cage after McGregor appeared to go for a finish. Alvarez was unable to penetrate, cut off the ring, or score a takedown. It was not the fight he scripted.

In the second round, McGregor stood in the center of the octagon and tucked his hands behind his back. He was so unthreatened, baiting Alvarez to attack. Alvarez did, and McGregor dropped him again with his left hand. The Philadelphian quickly recovered, but the biggest night of his career was coming to a close. He could not stay away from McGregor's left hand.

It was UFC's debut at Madison Square Garden after New York's state legislature made the sport legal in April. New York was the final state that had still banned MMA. And UFC wasted little time in trying to put on a show. The card featured three title fights.

Alvarez found himself in the main event after beginning his MMA career 13 years ago in a Frankford basement. It was quite the journey. He spent a decade in the sport's minor circuits before finally getting to UFC in 2014. Alvarez won the lightweight title in July and Saturday night was his first defense, against the biggest star in the history of mixed martial arts.

The night was the first time in six years that he fought within 300 miles of Philadelphia. The fight game had taken him to Mexico, Las Vegas, Canada, and California. At last, he would be home.  But Saturday brought little advantage.

Madison Square Garden might as well have been Dublin's Aviva Stadium. The crowd belonged to McGregor and his fans, who filled Manhattan's Irish pubs in the afternoon and paraded to the arena draped in tri-color flags. The first roar came before an undercard bout when the jumbotron flashed a McGregor video.

The final roar came hours later, when McGregor climbed the cage and hoisted his pair of UFC titles. Alvarez's big night had slipped away.