Jon Jones dominated Stipe Miocic in the main event of 309 ... and then shouted out President Trump during his post-fight interview with Joe Rogan, thanking him for attending.

Bones even started a "USA! USA!" chant ... and hit Trump's famous dance move before exiting the Octagon to talk to the president-elect.

Donald Trump, Elon Musk, and RFK Jr. walk into an arena ...

No punch line here -- just punches -- as the President-elect returned to the site of his pre-election rally, and brought some famous buddies!

The soon-to-be 47th U.S. President, flanked by close friend Dana White, walked to his Octagon-side seat with Elon and Bobby, as well as Musk's DOGE's partner, Vivek Ramaswamy, Tulsi Gabbard, DJT's pick for Director of National Intelligence, and Speaker of the House, Mike Johnson.

Kid Rock was also part of the squad ... which walked out to one of his hit songs. Eric Trump and Don Trump Jr. were also in the house.

The group took their seats just before the main card began at 10 PM ET.

Of course, Donald, who is a real-deal MMA fan, and Dana go way back. In fact, the UFC CEO told us on Friday that DJT may attend the MSG event.

Michael Chandler, who is fighting in the co-main event against Charles Oliveira, told us last week Trump told him he'd be at the fights if he won the election.