New York City Mayor Zohran Mamdani is partying like a champion on Thursday ... joining the New York Knicks on their float for their NBA Finals parade -- and showing off his moves that would make Fat Joe proud!!

The mayor was spotted right next to Karl-Anthony Towns during the massive gathering in Lower Manhattan ... and when the cameras cut to the duo, they did their best "Lean Back" dance as the man himself performed the hit song.

It's par for the course for this celebration ... as there are plenty of notable names sprinkled through the festivities. On top of the familiar faces, there are so many fans in attendance that officials said the area was at full capacity hours before the parade was slated to start.

Ben Stiller and Spike Lee were spotted along the route ... with the former documenting the scene on his phone.

Perhaps the most special moment for Mamdani, though?? He got to take a pic with Jordyn Woods' lucky bag, which recently sold out online!!

And yes, the drinks are flowing -- from beers to tequila, the floats are fully stocked with all the booze one could ever ask for.

Soak it all in, Knicks fans!!