Two late goals from Sporting Fingal dealt a hammer blow to Shamrock Rovers' title dreams at Tallaght Stadium.
Thomas Stewart put Rovers ahead from close-range after 13 minutes. Chris Turner then wasted a chance to double he lead when his penalty hit the crossbar on 64 minutes.
Gary O'Neill pounced on an error by Aidan Price to grab an equaliser in the 87th minute. Rovers' old nemesis Glen Crowe then snatched a winner in the final minute with a deflected strike.
Rovers only have themselves to blame as they had several chances to make the game safe in the second half and were hit by the ultimate sucker-punch.
They must now now rely on Bohemians slipping up in their final two games if they are claim their first Premier Division title since 1994.
The Gypsies moved one point clear at the top with a 1-0 win over St Patrick's Athletic earlier in the day.
The win keeps Fingal's chances of finishing in the top three alive as they have a game in hand on their rivals, Sligo Rovers and St Pat's Athletic.
Rovers began with the side started the second half against Bohs after Thomas Stewart replaced Paddy Kavanagh.
Liam Buckley made three changes from the 2-2 draw with St Pat's. In came goalkeeper Brendan Clarke, Kenny Browne and Shane McFaul for Darren Quigley, Ollie Cahill and Shaun Maher.
Cowe's goalscoring touch seemed to desert him when he wasted an early chance to put Fingal ahead. Conan Byrne skipped past Enda Stevens and whipped in a cross that dropped kindly for Crowe but he fired wide from six yards.
Fingal were made to pay for that miss when Stewart put the Hoops ahead after 13 minutes, although there was a suspicion of offside about the goal.
Billy Dennehy put Twigg through on goal but the striker chose to pass rather than shoot. Stewart tapped into an unguarded net as Fingal appealed for a flag that never came.
Stewart returned the compliment six minutes later, but Twigg could not keep his shot down. James Chambers was next to go close for the home side, but he too failed to hit the target after Stephen Rice had picked him out on the edge of the box.
Fingal's response was impressive as they continued their neat approach play, but it was not matched by a cutting edge in final third.
Byrne's deliveries were causing Rovers problems and Shaun Williams and Colin Hawkins both went close with headers from the winger's corners.
Fingal full-back Lorcan Fitzgerald kept the deficit at one when he charged down Craig Sives' shot on the stroke of half-time.
Twigg should have doubled the lead on 47 minutes when Chris Turner set him free, but the striker could only lob into the arms of Brendan Clarke.
Rovers were really pushing for a second goal and Stewart's clever pass put Dennehy through. However, he tried to be cute by returning the ball to Stewart and Fingal cleared.
Fingal were grateful to Clarke for parrying Dennehy's strike after the winger had skinned Ger O'Brien. At the other end, Mannus got down well to keep out Williams' dipping free-kick.
Rovers wasted their best chance to calm nerves when Clarke took down Turner for a penalty. Turner stepped up to take the spot-kick himself but he drilled it against the bar.
Clarke made amends for the penalty mistake when he produced a double save to deny Twigg and Stewart from close-range on 66 minutes.
Fingal then brought on Alan Kirby for Hawkins as they tried to force an equaliser and keep their European hopes alive.
The result could have gone either way in the final ten minutes of a game that tested nerves and ability.
Rovers were made to pay the ultimate price for their wastefulness in front of goal as Fingal snatched victory from the jaws of defeat.
Price dwelt on the ball after a poor header back for Rice and O'Neill used his predatory instincts to sneak in and flick the ball past a stranded Mannus.
In a cruel twist it was the man who Rovers fans love to hate who secured a dramatic win for the visitors. Crowe stunned the home crowd when his shot deflected off Price and past a helpless Mannus.
Shamrock Rovers: 1 Mannus; 13 Flynn, 4 Sives, 5 Price, 3 Stevens; 8 Chambers, 6 Rice, 18 Turner, 20 Dennehy; 23 Stewart, 9 Twigg.
Subs not used: 16 Jennings, 7 Bradley, 11 Fenn, 15 Kavanagh, 19 Murphy.
Sporting Fingal: 1 Clarke; 2 O'Brien, 5 Hawkins (15 Kirby '76), 6 Browne, 3 Fitzgerald (14 Cahill '82); 7 Byrne, 4 Williams, 8 Finn, 11 McFaul; 9 O'Neill, 10 Crowe.
Subs not used: 16 Quigley, 12 Gannon, 17 Quinn.
Referee: Declan Hanney.