Having previously not conceded a goal in championship football since April, Kilmacud Crokes leaked three at Parnell Park and came mightily closed to being dumped out of the AIB Leinster club SFC.
A fourth goal concession seemed a certainty in injury-time too when Portlaoise, trailing by three points, were awarded a penalty to level the game but Craig Rogers' kick was expertly saved.
Rogers had earlier came on and scored a goal in the 46th minute which tied the game and set up an exciting finale.
But that score proved to be Portlaoise's last of a highly entertaining semi-final as Crokes points from Pat Burke, Paul Mannion and Andrew McGowan ultimately separated the teams.
Crokes, who won the last of their four titles in 2010, will play Mullinalaghta of Longford in the final on December 9 in what will be a David versus Goliath encounter.
Yet joint managers Johnny Magee and Robbie Brennan will realise they have plenty of scope for improvement, particularly in defence.
Aside from that penalty miss, Portlaoise also hit 12 wides - nine in the first-half - and dropped a couple of score attempts short on a frustrating afternoon.
Both sides were committed to an open and attacking game and forwards dominated with Crokes racking up 1-11 in the first-half alone.
Back to back All-Star Mannion was tracked by Portlaoise full-back David Seale who held the Dubliner to 0-5 and just three points from play.
Dara Mullin was Crokes' best attacker initially and his early goal put them on the way with points also coming from Shane Cunningham, Craig Dias and Cian O'Connor.
Portlaoise had plenty of success off their own kick-out and dominated the middle third at times but couldn't make it pay on the scoreboard and rued all those first-half wides.
Gareth Dillon and Paul Cahillane pinched fifth and 17th minute goals to keep them in the game at half-time at 1-11 to 2-5 down.
The visitors were more efficient in the third quarter and wiped out the deficit when Rogers played a neat one-two and slammed in a 46th minute goal, levelling it at 1-14 to 3-8.
But they didn't score again and winced as Rogers' penalty kick was palmed around the post in stoppage time by Crokes 'keeper David Nestor.
D. Mullin (1-2); P. Mannion (0-5, 2 frees); C. Pearson, P. Burke (1 free) (0-3 each); S. Cunningham, C. Dias, C. O'Connor, A. McGowan (0-1 each).
P. Cahillane (1-3, 1 free); G. Dillon, C. Rogers (1-0 each); R. Maher, K. Lillis, B. McCormack, C. Boyle, B. Glynn (0-1 each).
D. Nestor; L. Flatman, A. McGowan, R. McGowan; C. O'Connor, C. O'Shea, C. O'Sullivan; C. Dias, C. Casey; S. Horan, C. Pearson, S Cunningham; P. Mannion, D. Mullin, P. Burke.
A. Jones for R. McGowan (36); K. Dyas for Horan (47); T. Fox for Cunningham (55); S. Williams for Mullin (62), R. Ryan for O'Connor (62, black card). Dias black card 65, not replaced.
G. Brody; F. Flanagan, G. Saunders, D. Seale; C. Healy, C. Finn, D. Holland; C. McEvoy, K. Lillis; B. Glynn, C. Boyle, G. Dillon; P. Cahillane, B. McCormack, R. Maher.
C. Rogers for Maher (36); S. Lawless for McCormack (47); A. Rafter for Glynn (55); C. Finn for Holland (58).
D. Coldrick (Meath).