Centre-forward Cein McMonagle was in fine scoring form as reigning All-Ireland champions St Mary's Edenderry qualified for the provincial final with a hard-earned victory in Mullingar.
McMonagle scored all of his side's 2-3 in the first half, including an opportunist goal in the 13th minute and a blistering drive to the roof of the net in the 25th minute.
Marist College's players and mentors thought they had a goal with the last kick of the half from Nicky Kelly, but the match officials decided that the ball had not crossed the line, leaving St Mary's ahead by three points, at 2-3 to 0-6, at the break.
When Ruairi McNamee poked home his side's third goal in the 47th minute, the champions led by five points (3-5 to 0-9) and looked assured of victory.
However, with Conor Marlowe outstanding, the Athlone lads fought back well and it needed a McMonagle free in injury-time to guarantee his side's place in the provincial decider.
Scorers – St Mary's: C McMonagle 2-5 (0-4f), R McNamee 1-0, S Moriarty, R Caffrey, O Lawton (f) 0-1 each. Marist College: N Neary 0-6 (6f), C Marlowe (2f), R Ashe, A Byrne (1f) 0-2 each, N McInerney, TJ Fox 0-1 each.
St Mary's – C Hurley; D Leech, M Kearney, A Mahon; R Mangan, S Moriarty, S Doran; L Flynn, R Caffrey; M Cleere, C McMonagle, P Connolly; I McKeon, D Pyke, R McNamee. Subs: J Mulranny for Connolly (35), D Kennedy for Mangan (39), O Lawton for Pyke (45).
Marist College – T Finnerty; B O'Donohue, E Quigley, M McArdle; C Marlowe, D King, R Ashe; S Omukoro, A Curley; TJ Fox, N Neary, M Monaghan; A Byrne, N McInerney, N Kelly. Sub: A O'Sullivan for Kelly (41).
Ref – C Reilly (Meath)