GREAT SCOTT!!!!!!!

The very first pair of the Nike Air Mag -- the Marty McFly shoe from "Back to the Future II" was auctioned off in L.A. last night ... and the winning bidder dropped $37,500!!!!!!!!!!!!!

The auction -- co-hosted by Joel McHale -- went down at the Montalban Theater ... and after an INTENSE stand-off between two shoe-a-holics ... the winner was eventually crowned.

Along with the shoes, the winner also received a "plutonium case" where he can store his "McFly's"

Oh, and McHale also promised to throw in a puppy ... we'll find out if he REALLY meant it.

So far, the identity of the buyer remains a secret ... we're guessing it won't be for long.

FYI -- all of the proceeds from the auction benefit the Michael J. Fox Foundation for Parkinson's Research.