Timothée Chalamet was riding an emotional roller coaster at Madison Square Garden ... and by the final stop, he was floating on air.

The diehard Knicks fan got swallowed up by a sea of celebrating New Yorkers after the team's jaw-dropping 107-106 comeback win over the Spurs Wednesday night in Game 4 of the NBA Finals.

Check out the video ... Timothée and fellow Knicks superfan Ben Stiller were mobbed by ecstatic fans as chants erupted and the postgame party spilled into the streets.

Timothée looked like he'd just won a championship himself, grinning from ear to ear and soaking in every second of the madness after New York erased a staggering 29-point deficit to take a commanding 3-1 series lead.

And Timmy wasn't the only one feeling the comeback fever. His girlfriend, Kylie Jenner, was all smiles inside the arena -- celebrating with hugs from both Jordyn Woods and Taylor Swift as the Knicks pulled off one of the wildest rallies in NBA Finals history.

Taylor didn't call game over at the final buzzer, either ... she kept the Knicks celebration going at Zero Bond with the Haim sisters, Hailey Bieber, Sombr and Tate McRae.

If the Knicks finish the job, Timothée might never come back down to earth!!!