Kevin Small scored with the last kick of Wednesday's semi-final replay to put Magherafelt school St Mary's into the 2017 MacRory Cup decider.
Small's stoppage-time free clinched victory after a marathon struggle against St Paul's of Bessbrook.
Just like the first meeting, which ended 1-12 each, the rematch at the Athletic Grounds was a tight affair.
Liam Quinn shot in the only goal 15 minutes into the second half after a St Mary's break down the right.
St Mary's will face St Colman's, Newry, in the final on 17 March.