Ballynahinch seconds drew first blood in the battle of the derby sides in Junior 4 and will be hoping to complete the double over the deadly rivals later in the season.
Young Matthew Martin was the star of the show for the visitors, scoring the all-important winner with just minutes remaining.
Ballynahinch went into the game missing four regulars who were all on duty with the senior side, but they played well in what was at times, a particularly scrappy affair.
The first real chance of the game fell to Down's Philip Brown in the second minute, but his effort flew past the wrong side of the post.
The visitors relied on the experience Marty Coulter, Stephen Hayes and Norman Brown at the back and, if truth be told, they were rarely troubled all afternoon and were able to wallow on the comfort zone as the home side failed to fire on all cylinders.
Down relied on the experienced Willie Price and Trevor Love in their back-line and while the former had to depart through injury, Love remained to play an integral role.
He defended when he had to and never failed to seize the opportunity to bomb forward to help set up attacks. In the closing stages when Down were looking for an equaliser, Love was in the tick of things in the penalty area.
Paul Martin then created a chance for Lee Duffield and the youngster, alongside Matthew Martin, was never found wanting in the heat of the derby battle.
In fact, Martin looked odds-on to score midway through the first half, but was denied by the tenacious Love who read the danger and cleared his lines.
In the middle of the park, Down relied on Colin Gibson and Raymond McClurg and while they battled gamely, others around them sometimes failed to read through-balls.
Cecil Telford was introduced into the action and had an immediate impact. One mazy run took him into the heart of the Ballynahinch area and his shot screamed past the wrong side of the post. Justin Sloan and Stuart Brown worked tirelessly for Ballynahinch, but it was no surprise the sides ended up all-square at the break.
After the break, Paul Martin rattled the crossbar after he was picked out by his son Matthew, while 'keeper, Johnny Briggs, kept Down in the game with a superb save minutes later.
Johnny Lennon nipped in to clear the ball from Jim Sloan who looked set to score, while at the other end, Stephen Moffatt should have done better with the goal at his mercy.
With minutes to go, Matthew Martin bagged the winner, but Telford almost earned his side a point with a ferocious short corner strike in the dying seconds of the game, but his rasper was kicked clear by Patterson.