'Eye of the Tiger' Singer LIVE & ACOUSTIC From Some Dude's Basement

7/25/2013 10:37 AM PDT

OK, this is pretty cool ... it's weird ... but it's cool.

Jim Peterik -- the original lead singer of the band Survivor -- busted out his nicest guitar, and his tightest white pants, and jammed out an acoustic version of "Eye of the Tiger" in a basement ... and it was awesome.

It all went down Tuesday night at a home in Chicago, where the guys from "Hardcore Pawn: Chicago" were holding a live chat for their fans.

Jim -- who was born in Illinois -- stopped by to hang out ... and while he was there, the 62-year-old rock legend busted out a rendition of his biggest hit -- you know, the song from "Rocky III."

Now, watch the video ... put on your finest track suit ... and go run up some stairs.

It's what Mickey would want ...