Tied 0-3 apiece at the break, thereafter the Cork champions underlined their superiority, particularly in the fourth quarter when Oola were reduced to 14 men.
The Limerick side had no answer to a more balanced Carrigaline outfit that overcame a tentative opening 30 minutes to win comfortably in the end.
Meanwhile, Oola were reliant on impressive 17-year-old midfielder Josh Ryan for all of their scores – with just the one from play.
“Up until the sending off it was tit-for-tat,” said winning manager Michael Meaney.
“We were the better football team but we were disappointed at half-time. We played our own game in the second-half and the goals were vital.
“In these conditions the least amount of mistakes counted and thankfully we came out with the right result.
“Our Achilles heel last year was giving teams soft scores at the end of games.
“We have worked on that. It was a team effort. The workrate of the middle eight is huge, lads working back. You have Nicholas (Murphy’s) experience. He is 37 now. And you must give credit to the younger lads as well who are stepping up, the likes of Kevin Kavanagh, Cian Barry, Barry O’Keeffe and David Drake. We are a senior team and they are the future.”
There was only one point from play in the first-half, and that was from Ryan.
Carrigaline’s three scores came from free-takers Brian Coakley and Drake (2). However, they kicked on from the restart.
Quick points from Coakley and captain Barry O’Keeffe were registered while Oola could only muster a Ryan free. Coakley then converted another placed ball before O’Brien did well to find the net right on the three-quarter mark — his initial effort saved by goalkeeper Kevin Nolan (1-6 to 0-4). Drake extended the lead to six points after Oola lost Daniel Quirke to a red card in the 50th minute.
The Limerick side were then hit with another sucker punch when Drake, who was picked out by sub Billy Pope, goaled from close range.
Brian Coakley got a second yellow card at the very end, but Carrigaline were already safely through to the provincial final.
“We will be coming up against a very good team,” added Meaney. “We saw the result, any team that scores 4-21, that is some achievement. St Mary’s are the team to beat.”
D Drake (1-3, three frees), S O’Brien (1-0), B Coakley (0-3, two frees), B O’Keeffe and E O’Connor (0-1 each).
J Ryan (0-5, four frees).
S Mellett; K Forbes, P Murphy, P Ronayne; C McSweeney, C Barry, S Griffin; N Murphy, E Kavanagh; Kevin Kavanagh, B O’Keeffe (Capt), E Ryle; S O’Brien, B Coakley, D Drake.
D Griffin for S Griffin (52 inj), B Pope for B O’Keeffe (56), E O’Connor for C Barry (57), M O’Reilly for E Kavanagh (59), Kieran Kavanagh for P Murphy (62).
K Nolan; S Whelan, E Fitzgibbon (Capt), F O’Grady; S Ryan, D Moloney, J Bourke; J Ryan, Conor Ryan; T Hayes, K Bourke, D Quirke; P Bourke, D O’Donovan, R English.
C Hennessy for C Ryan (40), D Stapleton for D O’Donovan (47 bs), D O’Donovan for P Bourke (51), Ciaran Ryan for S Ryan (64).
Sean Joy (Kerry).