Nineteen-year-old Mullins powerfully headed Billy Jones' cross home to give the ten man Harriers a shock 2-1 lead shortly after the hour mark.
Kidderminister, who remain three points adrift of safety sitting second from bottom in League Two, were 1-0 down and down to ten men after twenty-five minutes.
Yet the Aggborough based side fought back to secure a crucial victory that gives them hope of beating the drop.
Mullins, who scored an own goal on his debut for the club in a 2-0 defeat at Cheltenham last month, has made nine appearances for Kidderminister since making the loan move from Reading.
The youngster, who wears squad number 6. will remain with the Harriers for the rest of the season as they battle to avoid the plunge into the Conference.
Praising his side following their gutsy fightback, Harriers boss Stuart Watkiss admitted his team need to put in more performances like the one they did on Saturday if they are to avoid the drop.
"We're going to need that week-in, week-out if we're to get out of the situation we're in but if that's not a guiding point for them then nothing can be," he said.
"Tackles were won and players were throwing themselves in front of the ball but we've been here before. Its one game and we need to put a sequence of results together."