Shelbourne take over as league leaders as a result of this disappointing defeat for Waterford United at the RSC and the Blues are now out of contention and condemned to another season in the lower division.
The Reds and Dundalk will contest next Saturday’s day of reckoning when the championship title and the single promotion place will be decided on the last gasp of the campaign.
Shelbourne will be at home to Limerick 37 while Dundalk travel to face Kildare County.
Shelbourne broke the deadlock on 34 minutes when David McAllister scored from the penalty spot following a period of intense pressure on the home goal.
United had failed to clear their lines from a David Freeman corner and, as the ball bobbled about in a crowded area, referee Robert Rogers adjudged that the Reds’ skipper Damien Brennan was upended by Dave Warren.
United enjoyed the best of the exchanges for the first fifteen minutes and David Grincell went close to scoring on two occasions. But then the visitors began to dominate, especially at midfield, and Anto Flood had the ball in the net on 24 minutes, only to be ruled offside.
Minutes later, James Keddy unleashed a powerful blockbuster from 30 yards which Packie Holden did well to tip over the United crossbar for a corner.
United’s Kenny Browne was dismissed on 90 minutes for a second yellow card offence.
Waterford United: Holden, Quigley (Dunphy, 58 minutes), Clarke, Fitzpatrick, Browne, Warren, Fitzgerald, McCarthy (Bermingham, 81 minutes), Sullivan (Kiely, 78 minutes), Grincell, Waters. Substitutes not used: Mulcahy, Spicer.
Shelbourne FC: Delaney, Murphy, Hedderman, Keely, Brennan, McAllister, McGill, Keddy, Flood, Freeman, Rutherford (Chambers, half-time). Substitutes not used: Georgescu, Byrne, Lawrance, Whelan.
Referee: Robert Rogers, Dublin.