LAS VEGAS - Conor McGregor backed up every word he ever said to Jose Aldo with one spectacular punch.
McGregor stopped Aldo with a left hand to the jaw just 13 seconds into the first round Saturday night, claiming the undisputed featherweight title at UFC 194.
McGregor (19-2) finished the fight with an electrifying exchange shortly after the opening bell, slipping Aldo's lead right and cracking the champ with his formidable punching power.
Aldo (25-2) actually finished his punch and hit McGregor with a left, but the champ fell senseless to the ground. McGregor pounced, only to be pulled off in his fifth consecutive knockout victory.
"What I say happens, happens," McGregor said. "There is no doubt now."
Aldo had won 18 consecutive fights over the last 10 years, but not even the only previous 145-pound champion in UFC history could survive McGregor.
The loquacious Irish brawler goaded Aldo throughout the promotion of their delayed bout, only to earn a victory that was even more dramatic than he predicted. McGregor's victory was the fastest title fight in UFC history, surpassing Ronda Rousey's 14-second win over Cat Zingano at UFC 184 in February.
"Precision beats power, and timing beats speed," McGregor said. "Jose was a phenomenal champion. He deserved to go a little bit longer, but I still feel at the end of the day, precision beats power and timing beats speed. That's what happened."
Luke Rockhold also claimed the UFC middleweight title with a bloody fourth-round stoppage of previously unbeaten champion Chris Weidman in front of a frenzied crowd at the MGM Grand Garden Arena.
But the sellout crowd was packed with thousands of screaming Irish fans who traveled to see whether their braggadocious countryman could back up his talk. The fans celebrated long after McGregor left the cage, singing and carousing and forming a lengthy conga line.
McGregor, a former plumber who was fairly late to take up mixed martial arts as a career, has won 15 consecutive fights since November 2010 while building an international celebrity on his combination of MMA skill and verbal dexterity. He is 7-0 in UFC bouts, stopping all but one opponent with his vaunted punching power.
McGregor picked one of the UFC's most daunting targets in Aldo, who had made seven consecutive title defenses. The Irishman targeted the imperious Brazilian champion with a steady stream of trash talk and entertaining antics, infuriating Aldo while making himself into a pay-per-view draw and arguably the UFC's second-biggest star behind Rousey.
McGregor and Aldo were scheduled to meet at UFC 189 in July, but Aldo pulled out with an injury two weeks before the bout. McGregor stopped Chad Mendes in sensational fashion to win the interim title belt but never stopped talking about Aldo.
Aldo hadn't fought since October 2014 due to injury. After recovering from the knockout, Aldo called for a rematch in the cage, saying through an interpreter that it "wasn't a real fight."
"The trash talking didn't affect me," Aldo said. "I don't care what he says."
For just the third time in UFC history, two undisputed title belts changed hands on the same card.
Rockhold (15-2) finished his own championship victory with brute style, pounding Weidman on the ground late in the third and again in the fourth. When referee Herb Dean finally pulled Rockhold off the bloodied Weidman (13-1), the new champion collapsed face-down on the canvas in relief.
"It's hard to take this all in," Rockhold said. "I went through hell to get here, but it's all worth it now."
Rockhold, a native of Santa Cruz, California, has stopped his last five opponents.
He seized control of the fight when Weidman attempted to throw a wheel kick in the third round. Rockhold dodged it and took the champ to the ground - the first time Weidman, a renowned wrestler, had ever been taken down in a UFC fight.
"He shouldn't be trying that kind of stuff on me," Rockhold said.
Weidman had ruled atop the division since dethroning long-reigning champ Anderson Silva in 2013 and breaking Silva's leg in the rematch. Injuries limited Weidman's activity, but Rockhold established himself as the clear No. 1 contender with four straight UFC victories since a testosterone-aided Vitor Belfort stopped him in Rockhold's only loss in 14 fights since November 2007.
UFC 194 concluded an unprecedented three-day stretch of three fight cards on the Las Vegas Strip.
Yoel Romero won an entertaining split decision over Ronaldo "Jacare" Souza in a meeting of middleweight contenders. Demian Maia also dominated Iceland's Gunnar Nelson with his peerless jiu-jitsu to win a wide decision, and veteran bantamweight Urijah Faber finished the preliminary bouts with a bruising win over Frankie Saenz.