It all went down at Zion's high school gym in Spartanburg, SC -- where he's put on a few dunk shows this summer.
The Duke commit took a running start from one side of the court ... planted his toes on the free throw stripe -- and stretched out like M.J. in Space Jam for the throwdown.
FYI ... it's 15 feet from where Z took off to where he landed ... and for good measure -- he put down a left-handed windmill to show it was no fluke.
No word on Coach K's thoughts yet ... but we're callin' it here -- that's impressive!!