The clause was put in after he netted eight times last season, but this goal was the first this time around.
It came courtesy of a clever chip from Sammy Igoe and sent the Stags - who had looked the better side - down to only their second defeat in nine games.
Disley, who played 141 games for Mansfield before changing clubs, had been struggling in an indifferent midfield but ended up his club's hero.
Goals usually flow when these teams meet - 18 in the last four - so this one must go down as a game of false pretences.
Mansfield arrived with their confidence high and shaped to roll over a side with the least number of goals in the league. But for all their pacy moves around the box they came up against a Rovers' defence in a mean mood.
Their powerful middle line took control but Mansfield managed just one shot in the first half and that came from right-back John Mullins who blasted an injury time shot over the bar.
Things were no better for Rovers, their one effort on target coming from centre-back Steve Elliott with a far post header from a corner.
Stags boss Peter Shirtliff was forced into one change breaking the partnership of Danny Reet and Richard Baker which has given him 17 goals so far.
Reet had played for 20 minutes with a bandaged head after a midfield collision.
His replacement a lively Mike Boulding featured in three incidents in his first 10 minutes on the pitch which could have broken the deadlock.
First he was fouled by Elliott just outside the box, Mullins sending his free kick a shade too high.
Then as he burst through on the right Byron Anthony dived in with a well judged tackle to stop him but the best chance came a minute later down the other flank.
Giles Coke, calmly lifted the pass over defenders to put Boulding in with a clear shot when it came it was foiled by Steve Phillips' brilliant dive.