But for Kilsyth, who reached the Super League First Division safety mark a couple of weeks ago, the defeat almost certainly ended any faint hopes they had of making the promotion play-off.
Cumbernauld had won both previous derby clashes this season - in the league and the Sectional League Cup - but Rangers looked the livelier side at the start.
Damon Welsh had a good opening in the first few minutes but his finish was weak.
In only 10 minutes though they went ahead. Cumbernauld ’keeper Barry Fraser only succeeded in palming a fierce shot out and Nicky Prentice, following up, headed the ball in.
Their lead was to be shortlived though.
A foul in the Rangers box resulted in a penalty and Dale Clark sent stand-in Kilsyth ’keeper Keenan the wrong way to level the scoreline.
Keenan had only been called in hours before the kick-off by Rangers who then lost defender Chris Reid who pulled up in the pre-match warm-up.
And they suffered a further blow when Joe Barclay had to leave the field, replaced by Paul McBride.
The game was being played at a pretty pedestrian pace and there was not much to excite either set of fans.
Chances fell to both sides but neither was able to get in a decent shot in a pretty even first half with play seldom rising above mediocrity.
Rangers briefly had the upper hand from the restart and a couple of good openings fell to sub McBride but his efforts were wildly off target.
Cumbernauld made a couple of changes, bringing on Steph McDonald and Kieran Brown, and started to get a grip on the game, but most of their efforts were no better, although Keenan made a good stop on the line off a shot by Brown.
There were a few bookings by the referee although it was not really a very bad tempered affair.
Rangers made another change, bringing on Michael McGee for Corey Pearson, and United also made a final substitution, bringing on Kris Irvine.
And this was to prove to be a match winning decision as Irvine won the ball in the Rangers half, rounded a defender and the unfortunate ’keeper, and fired a good shot into an empty net with around three minutes left.
United celebrated wildly, and rightly so, as they and deserved their win.
They have given themselves a great chance of escaping relegation and although they have a couple of tough matches to come, it is in their own hands and with this attitude they should see it through.
Kilsyth on the other hand played this match as if it did not really matter how they finished from that point onwards and a big change in attitude is needed if they are ever to reach the higher echelons of league status.