A Mark Russell brace stunned Bohs at Dalymount Park on Saturday to keep Finn Harps' automatic Premier Division survival in their own hands.
Second-placed Bohemians' surprise defeat meant arch-rivals Shamrock Rovers were crowned champions without having kicked a ball in over three weeks.
The result also confirmed Cork City's relegation, and Harps have now been beaten only once in seven games.
Though Shels are five points ahead with one game to play, Harps have two games in hand, and all three of their remaining matches (against St Pat's Ath, Shamrock Rovers and Waterford) are at home.
"It was a massive win," said Harps' defender Dave Webster. "But given the performances we've produced in recent games we felt it was coming. We were professional and saw it out well."
Harps took the lead in first half stoppage time when Bohs failed to clear Tony McNamee's long throw. Kosovar Sadiki headed the ball back goal-ward where Russell flicked it past James Talbot.
The visitors added to that six minutes into the second half.
Adam Foley's cross from the right found Russell and the winger's drive took a slight deflection to nestle in the far corner of the net.
Mark McGinley in the Harps goal made terrific saves from Danny Grant, and twice from Evan Ferguson, before Bohemians left-back Anto Breslin received a straight red card after being adjudged to have kicked out at Leo Donnellan on 74 minutes.
Donnellan was then also sent off for a rash challenge on James Finnerty with five minutes to go.
Next up for Harps is the visit of St Pat's on Wednesday. "We've given ourselves a real chance. Three massive games, all at home," added Webster. "All we can look at is St Pat's. They're pushing for Europe, so it's going to need another massive performance to get three points."
Bohemians - Talbot; Lyons, Finnerty, Barker, Breslin; Buckley (Lunney 88), Levingston (Devoy 56); Omochere (Moylan 56), Ward (Tierney 56), Grant; Wright (Ferguson 56).
Finn Harps - McGinley; McEleney, Sadiki, Folan; G. Harkin, Donnellan; Webster, T. McNamee (Connolly 72), Russell; O'Sullivan (Foley 16; Cretaro 90+4)), B. McNamee.
Ref - N Doyle (Dublin)