Deion Sanders just GUARANTEED he'd bring victories to Jackson State after accepting the HBCU's head football coaching job -- and his speech promising the Ws was epic!

Prime Time was introduced as the school's new head man Monday morning at a raucous pep rally on the Mississippi campus ... and it didn't take long for Deion to fire up the crowd.

The NFL legend spoke for about 10 minutes ... and said point-blank JSU is going to win PLENTY of football games under his watch.

"We going to win," Sanders said. "We going to look good while we win. We going to have a good time while we win. And we going to do this professionally."

In fact, the 53-year-old said his program is going to be so good ... he promised it'd lift up every other sport on the campus as well!!!

"I believe this is going to be a marriage made in heaven," Sanders said, "and I cannot wait to get started."

Deion added some Prime Time flare to his speech ... rockin' a custom suit that had JSU patches not only on the outside -- but in the lining of his jacket as well!!

The school, meanwhile, says it's PUMPED to add the Hall of Famer to its football program ... with university officials saying they have championship expectations with Deion at the helm.