Tito Ortiz says he's been DREAMING about revenge on Chael Sonnen for roughly 20 years ... ever since Chael "ruined" him during a college wrestling match ... and the time for payback is now.
Tito tells TMZ Sports ... back before they became MMA superstars, the two faced off when Tito was wrestling for Cal State Bakersfield and Chael was an Oregon Duck.
Tito says Chael caught him in a headlock and pinned him, and it "ruined me" -- leaving him wondering if he'd ever get a shot at redemption.