The Carrick side triumphed by 0-10 to 0-7, despite David McSharry shooting the Gaels into a 0-7 to 0-3 after 42 minutes.
St Mary’s closed the gap to the minimum with scores from Alan Doherty, Robbie Lowe and Conor McWeeney in the space of four minutes.
Following that, neither side scored for 11 minutes until St Mary’s sub Jimmy Guckian levelled with a 57th minute point.
Just prior to Guckian’s score goal chances were missed by the defending title holders through Peter McGowan and Stephen McGurrin.
St Mary’s took the lead for the first time on the stroke of full time with an Alan Doherty point. Then, in injury time, the Carrick men made victory secure and nailed a place in the semi-final against Carrigallen with points from Robbie Lowe — the only score from a free in the game, and Doherty.