Eric Musselman is a man of his word — the Razorbacks head coach partied shirtless after a HUGE upset win over #1-ranked Auburn on Tuesday night … and it was epic!!

Here's the deal — Muss met with a group of Arkansas students outside Bud Walton Arena in Fayetteville before the game … and was asked if he would do a topless celebration if they knocked off the top team in the country.

Not only did coach make the promise, he kept it after Arkansas knocked off Auburn, 80-76 … ripping his shirt off and celebrating like crazy!!