Jon Jones sent Stipe Miocic into retirement with a stunning back kick to the ribs and used a series of blows to the head in the third round to retain the UFC heavyweight championship in front of President-elect Donald Trump in the main event of UFC 309 at Madison Square Garden.

Jones posed and played to the crowd on top of the octagon in front of Trump, Elon Musk, picked by Trump to lead a new Department of Government Efficiency, and Robert Kennedy Jr., Trump's choice to lead the Department of Health and Human Services in his incoming administration.

Trump walked out to a rousing ovation in front of 20,200 fans just before the start of the pay-per-view card and seemed to bask in thrill of the fighters that throughout the night gave him props — including Jones.

"I want to give a big, big thank you to President Donald Trump being here tonight,” Jones said to a roaring ovation that bled into a "USA! USA!" chant.

"I'm proud to be a great American champion," Jones said.

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President-elect Donald Trump greets Jon Jones after he defeated Stipe Miocic at UFC 309. (Source: Associated Press)

Widely considered the best fighter in the world, Jones (28-1-0; 1 NC) was the aggressor from the start and landed a series of shots to Miocic's head in the first round. Jones showed he had plenty of fight left in the tank.

British heavyweight Tom Aspinall looms as the next challenger for Jones. Aspinall won a fight for the interim heavyweight title last November in the Garden. UFC chief executive Dana White had promised Aspinall, who chatted with Arizona Cardinals QB Kyler Murray, would challenge the winner of the main event in a unification bout.

"As far as my future in the octagon, I decided that maybe I will not retire," Jones said. "I know that we have options."

Miocic (20-5) failed in his bid to win the heavyweight crown for a third time and immediately announced his retirement.

"I'm done," Miocic said. "I'm hanging 'em up."

Stipe Miocic, right, punches Jon Jones in a UFC 309 mixed martial arts heavyweight title bout. (Source: Associated Press)

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In a lightweight bout that made every fan from Kid Rock to Jordan Knight to Anthony Kiedis go wild at the finish in the fifth round, Charles Oliveira beat Michael Chandler via unanimous decision. The fight was a rematch of their May 2021 fight when Charles Oliveira topped Chandler to win the lightweight title. Oliveira staked his claim to another title fight with the win.

The fifth round was about as good as it gets inside the octagon highlighted by Chandler dropping Oliveira twice on his back. The 38-year-old Chandler stepped inside the cage for the first time in two years, in large part because he waited for a fight that never materialised with Conor McGregor.

"We've been wondering where you've been, Conor," Chandler bellowed in the cage. "Come back and beat me if you can."

McGregor has been sued by a woman who accused him of sexually assaulting her in a Dublin hotel in 2018.

Chandler shook Trump's hand after the fight on a card more charged with politics than punches.

Meanwhile, Bo Nickal topped Paul Craig by unanimous decision in a welterweight fight, then crouched to speak to Trump. Nickal later said he wanted to golf with Trump.