Cha Dwyer hit an injury-time winner for 14-man Laois to give their top-tier survival hopes a huge shot in the arm.
Antrim had come from six points behind to lead during the final moments of normal time, but defeat means they will now enter a league relegation play-off should they lose to Tipperary.
Jack Kelly was dismissed for striking on 24 minutes, the toll of which seemed to finally tell on the hosts at O'Moore Park — before PJ Scully levelled matters ahead of Dwyer’s winner.
Antrim flew out of the blocks with the first three points of the game through Neil McManus (free), Michael Bradley and Conal Cunning.
After strong performances in defeat to Kilkenny, Dublin and Waterford, it hinted at a brighter afternoon for Darren Gleeson’s team.
By the end of the half, they were six points in arrears to a Laois side that had goals on their mind.
James Keyes hit a tame attempt early on but, after five minutes, Paddy Purcell raced onto a breaking ball, headed for the penalty area, and fired to the net from a tight angle.
The sides then traded scores as Stephen 'Picky’ Maher, Keyes and Dwyer did the needful for the O’Moore County, while Seann Elliott and McManus frees kept the Saffrons in the hunt.
Then came the decisive moment of the half as Kelly drove forward and won a free on 24 minutes, but was red-carded for swinging back after the whistle had been blown.
Seamus ‘Cheddar’ Plunkett’s men didn’t panic, however, and won the remainder of the opening period by 0-05 to 0-01 with scores through Maher, Enda Rowland (free), Willie Dunphy, and long-range pearlers from Purcell and Keyes.
Gleeson brought on Conor McCann and James McNaughton at the interval to inject a fresh attacking impetus, and his side replied with three quick scores to make it 1-11 to 0-11.
After creating 24 scoring chances in the first half — converting just half of those — Laois managed only two Maher frees in the opening 14 minutes of the second half.
McManus necklaced together three more placed balls for Antrim during that time, added to by a fine Bradley strike.
Down a man, Purcell began to exert an influence in his own half by dropping deeper during the second half.
It didn’t fully stop the Antrim surge as Gerard Walsh and Ciaran Clarke hit points, but Laois steadied the ship thanks to Dwyer, Dunphy, and a sideline cut from substitute Scully.
After relegating the Saffrons to the Joe McDonagh Cup in last year’s championship play-off, it looked as though Gleeson’s side would exert a measure of revenge when Eoghan Campbell, Cunning and Paddy Burke gave them the lead heading into the final minutes.
Instead, Laois came roaring back through a 60-yard sideline free from Scully, before turning over a short puck-out to fire over a winner through Dwyer.
Laois: Enda Rowland (0-01, 1f); Diarmuid Conway, Sean Downey, Podge Delaney; Liam O’Connell, Ryan Mullaney, Mark Dowling; Jack Kelly, Fiachra C Fennell; Paddy Purcell (1-01), James Keyes (0-02), Ross King; Willie Dunphy (0-02), Cha Dwyer (0-04), Stephen Maher (0-08; 4f, 2 ‘65)
Subs: PJ Scully (0-02, 1f) for Dowling (50); Aidan Corby for King (56); Stephen Bergin for Maher (71)
Antrim: Ryan Elliott; David Kearney (0-01), Gerard Walsh (0-01), Stephen Rooney; Paddy Burke (0-02), Eoghan Campbel (0-01), Ryan McGarry; Keelan Molloy, Daniel McKernan; Michael Bradley (0-02), Domhnall Nugent, Conal Cunning (0-02); Seann Elliott (0-01), Neil McManus (1-07; 7f), Ciaran Clarke (0-02)
Subs: Conor McCann for Elliott, James McNaughton for Nugent (HT); Conor Johnston for Kearney (59); Eoin O'Neill for Molloy (62); Ryan McCambridge for Bradley (69)
Referee: Shane Hynes (Galway)