Michael Graham and Robert Greer helped Ballynahinch win at Ballymacarn Park
Ballynahinch clinched a place in the AIB Cup Final by shocking Garryowen 24-17 in Saturday's semi-final.
Gerry Hurley's early try put Garryowen ahead but Stuart Lambe's touchdown enabled Hinch to level.
A Conor Gilroy penalty put Garryowen 10-7 ahead at half-time but Kyle Corrigan and Aaron Ferris tries put Hinch in control.
Ryan Banbry brought his tally up to 14 points with a penalty and Hinch held on despite Garryowen's late try.
Cork Constitution will face Ballynahinch in the decider after they defeated Young Munster 27-13 in Saturday's other semi-final.
Division 2 promotion-chasers Hinch had already beaten two Division 1 outfits on their way to the last four, but most pundits expected in-form Garryowen to be a bridge too far despite the Ulster club's home advantage at Ballymacarn Park.
Garryowen, third in Division 1, went into the game after nine straight wins and they made the better start with scrum-half Hurley burrowing his way over and the extras followed from Gilroy.
However, Ballynahinch fought back to produce a series of attacks, with Willie Faloon prominent, and they were on terms with Banbry added the conversion after Stuart Lambe's try.
Garryowen, cup winners two years ago, lifted the siege with a Gilroy penalty helping lead to lead 10-7 at the interval.
However, the third quarter proved decisive as Hinch scored two converted tries.
Lambe's superb break set up a try for Corrigan and Stuart Morrow's charge lead to Ferris' try, which was again converted by Banbry.
Another Banbry penalty extended Hinch's lead to 24-10 as they looked to have killed off Garryowen.
However, the Limerick side fought back in the closing stages with Diarmuid McCarthy's try helped to cut the Ulster side's lead to 24-17.
Garryowen produced further late pressure but Hinch held on to claim another famous victory.