Conor McGregor leaves the octagon after his first-round knockout victory over Jose Aldo in their featherweight title fight during UFC 194 on Saturday night in Las Vegas. (Steve Marcus/Getty Images)

You’d think UFC championship belts were easy to come by or something. Two of them changed hands Saturday night. One brutally. One breathtakingly.

After Luke Rockhold had bruised and battered Chris Weidman on the way to a fourth-round TKO to take away the middleweight belt, Conor McGregor put an exclamation point on a heart-pounding evening by handing Jose Aldo his first loss in 10 years, knocking out the Brazilian in just 13 seconds to seize the featherweight strap in the main event of UFC 194 at the MGM Grand Garden Arena in Las Vegas. It was the fastest title fight finish in UFC history, edging Ronda Rousey’s 14-second submission of Cat Zingano in February.

McGregor’s performance was stunning. The 27-year-old Irishman has talked the talk ever since he first stepped into the UFC cage 2 1/2 years ago. He’d done some robust walking of the walk, too, winning on all six of his previous trips inside the octagon, five times by knockout. But on this night he made the most glorious walk of all, sauntering out of the arena in possession of an armful of accolades: He’s the 145-pound champion, he’s the one who slayed a feared champion and pound-for-pound elite who had reigned seemingly forever, and he’s inarguably the biggest fighting star in the UFC.

This walking of the walk was just a short stroll. McGregor trotted out of his corner and took immediate residency at the center of the octagon, and as soon as Aldo was within firing range the challenger threw a straight left hand. It missed. But he followed with a leg kick and kept his lethal left cocked. And when Aldo surged forward and started to unleash a left of his own, the Irishman already had one on the way while he was moving backward. Both punches connected, but McGregor’s landed first, taking the steam off of Aldo’s. And taking the consciousness out of the 29-year-old Aldo himself.

Luke Rockhold, above, bruised and battered Chris Weidman on the way to a fourth-round TKO to take away the middleweight belt Saturday night. (John Locher/Associated Press)

The champion fell flat on his face, stunned and stiff, and the challenger pounced with a couple of hammer fists before referee John McCarthy could jump in. Thirteen seconds. And new UFC champion of the world. . . .

“Again, nobody can take that left-hand shot,” said McGregor (19-2). “He’s powerful and he’s fast. But precision beats power, and timing beats speed. And that’s what you saw there.”

McGregor’s analysis was as on-the-mark as his punches were. I mean, punch. Singular.

Aldo (23-2) had been the only 145-pound champion the UFC ever knew. He was awarded his belt five years ago when the sister promotion where he reigned, the WEC, was merged with the UFC. The Brazilian, 29, had won the WEC strap in 2009, and Saturday night’s fight was his ninth defense as WEC/UFC champ.

It was supposed to happen back in July, amid much pomp and circumstances. The loquacious McGregor had been campaigning for a shot at Aldo ever since he arrived in the UFC, and for 12 days last spring, his bold words and antics had fueled a UFC promotional tour that took the fighters to acrimonious joint appearances in eight cities in five countries. But then Aldo broke a rib in training, the title fight was off and McGregor instead took a short-notice tussle with tough contender Chad Mendes, knocking him out in two rounds. That set up Saturday’s showdown, which was the culmination of a glorious/grueling three-day Vegas marathon for the UFC and its hardiest of hardcore fans. Fight cards on Thursday, Friday and Saturday added up to 34 bouts.

The penultimate one, Saturday’s co-main event, featured another man who once slayed a Brazilian legend. Weidman had reigned in the 185-pound division ever since he smashed Anderson Silva in 2013. And he started strongly, controlling Rockhold (15-2) for much of the first round. But the challenger took over from there and the champ lost steam, and when Rockhold dodged a spinning wheel kick and turned it into a takedown in the third round, it was a first — the only time Weidman (13-1) had been taken to the canvas. The beatdown that followed nearly ended the bout, and when the round ended, Weidman wobbled to his corner.

The end was near, and it came after a second Rockhold takedown left Weidman exhausted and defenseless until the bout was waved off at 3:12 of the fourth. There was a new champion. And in mere minutes, there would be two of them.