MIAMI — Israel Adesanya, as he made his way toward the Ultimate Fighting Championship octagon on Saturday night for a pivotal championship rematch against a bitter rival, stopped and put a hand on the shoulder of Eugene Bareman, his longtime coach.
Bareman pointed to his head, a gesture to remind Adesanya to be smart. Adesanya had nearly defeated that rival, Alex Pereira, convincingly last November before a sporadic sequence led Adesanya to lose his 185-pound belt and his glare of invincibility in the middleweight division.
About 10 minutes later, after another chaotic exchange, Adesanya smiled as he stood over and mocked Pereira, who lay on the canvas unconscious while his family sobbed in their nearby seats.
Adesanya, using two powerful right punches while against the fence defending an attack, knocked Pereira out cold in the second round of U.F.C. 287, in front of a rollicking, star-studded Miami crowd. With those precise shots, Adesanya regained the middleweight championship and brought a dose of stability to a league that had seen several champions fall in recent months.
“A lot of people will try and write me off, but people still called me ‘champ,’” Adesanya told reporters after the bout. “I’m still a champion and I still carried myself like a champion.”
The outcome was different, but the parallels to the previous fight between Adesanya and Pereira were clear.
Then, at U.F.C. 281 at Madison Square Garden, Adesanya tripped in the cage in the fifth round and Pereira pummeled him as he retreated to the fence, earning a technical knockout when the referee stopped the flurry of punches. Adesanya had been leading on the judges’ scorecards when Pereira won.
In the second round on Saturday night, Adesanya again wobbled on his legs, this time because of a kick to his lower left leg by Pereira. Adesanya again retreated to the fence as Pereira pressured him with blows to his body and a glancing knee to the head. Yet this time Adesanya, who said he was intentionally baiting Pereira, found an opening and followed through with two counter right punches, which knocked Pereira to the canvas. Adesanya got in a final hammer fist as the referee stepped in.
Immediately, Adesanya stood over Pereira and mimed shooting arrows at him with a bow, using Pereira’s signature celebration against him.
The reversal added yet another layer to their long rivalry. Pereira had beaten Adesanya twice in the earlier stages of their careers on the kickboxing circuit, and said he was motivated to move to mixed martial arts in part by an interview Adesanya gave in which he profanely wrote off Pereira as no longer a serious fighter.
Adesanya had been the U.F.C.’s 185-pound division champion since 2019 and defended the belt five times, becoming one of the promotional company’s biggest stars in the process. His defeat in November to Pereira aligned with a string of upset losses for longstanding champions.
In August, at U.F.C. 278, Leon Edwards beat Kamaru Usman, the former 170-pound champion, by knocking him out via head kick after being down on the judges’ scorecards. Usman had been one win away from tying the U.F.C. record for consecutive victories (16). Usman lost to Edwards again in the rematch last month in London.
Also in March, Valentina Shevchenko lost the women’s belt for the 125-pound division when Alexa Grasso, who entered the fight as a 6-to-1 underdog, submitted Shevchenko by a rear-naked choke in the fourth round. Shevchenko won the flyweight belt in 2018 by dethroning another dominant champion, Joanna Jedrzejczyk, and defended the title seven times across a nearly five-year span.
“That’s just the game,” Adesanya said when asked about the turnover among recent champions.
Until the rapid ascent of Conor McGregor, fueled by his charismatic, brash personality and frequent knockouts, the U.F.C. created its fan base by marketing champions with elongated title runs such as Anderson Silva, Ronda Rousey and Jon Jones. McGregor himself became the sport’s biggest star at a time of upheaval when he knocked out the longtime featherweight champion Jose Aldo in 13 seconds in December 2015. Yet instead of defending his belt repeatedly like those before him, McGregor sought to fight in several divisions and to create bouts based on star power rather than divisional progression.
In an interview on Thursday, the U.F.C. president, Dana White, said he was unconcerned about the recent champion upsets’ hurting the promotion’s ability to continue growing in the mainstream. He said the unpredictable results were a natural factor of the sport that could help fans become more invested.
“They get built up more when they become dominant and everybody gets to know them, but when they lose, it’s so shocking and it reverberates around the world,” White said. “Then people want to see if the new champ can defend the title or if the old champion can regain it. It’s always a great story.”
Adesanya was arguably at the height of his fame in November when he headlined at Madison Square Garden, a venue for which the U.F.C. generally produces one of its strongest cards of the year. But his loss to Pereira did not seem to drastically hurt his stock.
Fans still cheered for him loudly throughout the week while booing Pereira. Adesanya entered the fight as a slight betting favorite while celebrities like the rapper Drake and the retired N.F.L. player Brandon Marshall publicly supported him. The knockout played out in front of a crowd that included at least six star N.F.L. players, including the receivers Odell Beckham Jr. and Justin Jefferson, as well as Donald J. Trump, the former U.S. president who pleaded not guilty recently to 34 counts of falsifying business records in connection with a hush-money payment to a porn star.
White, who sat cageside with Trump, the former boxer Mike Tyson and the musician Kid Rock, said Miami would become an annual destination, similar to New York.
“We need to come back to Miami,” White said.
The event took place amid major changes to the U.F.C. as a company. Last week, Endeavor, the media conglomerate that owns the U.F.C., announced that it had acquired World Wrestling Entertainment and planned to merge the two combat powerhouses into one company.
White, who will remain in his role with the U.F.C., said he did not envision much crossover between the U.F.C. and W.W.E. products and athletes, saying that the move would have a more tangible impact on the W.W.E.’s business considerations, including its budget, sponsors and upcoming negotiations for its television rights.
“They’re going to do what they do,” White said. “We’re going to do what we do.”