The hundreds of thousands of Kansas City supporters in attendance at Union Station couldn't wait for the tight end to hop on the mic at the championship celebration -- and, initially, it looked like he was going to deliver a speech for the ages.

The 34-year-old started to lead the crowd in a chant that accompanies the Tomahawk Chop ... before he called an audible, and tried to get everyone to sing Garth Brooks' hit song along with him.

Quickly, however, it became apparent Kelce was a little too overserved to get through the whole tune ... as he mixed up words and stumbled repeatedly.

He tried to make things right by going to his phone for the lyrics ... but even that didn't seem to do the trick.

Ultimately, Mahomes bailed him out by singing the song's chorus ... before he gave up -- and handed the microphone off to the show's host.

Up until that point, most of the rest of the Chiefs seemed fairly composed -- Mahomes spoke to the crowd about getting back to this point next season ... while star defensive end Chris Jones guaranteed he won't be moving on from Kansas City in free agency.

As for where Kelce goes from here, it's unclear ... as his girlfriend, Taylor Swift, is in Australia -- while he's obviously in need of some water and a nap.