Dundalk's faltering title defence looks all but over as they fell to a 2-1 defeat to Shamrock Rovers in Tallaght Stadium, the venue of arguably their greatest achievement in sealing passage to the Europa League group stages eight months ago.
The Lilywhites fell to their second defeat in the space of a week, and their fifth of the season, as they dropped to third place and 15 points behind runaway league leaders Cork City, who beat Finn Harps 5-0.
Ronan Finn, one of the starting line-up when Dundalk defeated BATE Borisov that night in Tallaght, and David McAllister scored the goals as the home side ran out comfortable winners.
Finn opened the scoring from close range midway through the first half before McAllister sent Rovers in two to the good with a header just before the break, before Niclas Vemmelund posted a late consolation.
Both sides tested the opposition goalkeeper from free kicks in the opening period, Graham Burke forcing a routine stop from Gary Rogers before Tomer Chencinski pushed a goalbound Michael Duffy effort over the top.
And McAllister had the net rustling with 11 minutes on the clock when he showed outstanding technique to volley first time from the edge of the box, but it was the side netting he found.
There were 17 minutes on the clock when Simon Madden showed pace and skill to get to the endline and pull back for Finn, who finishes clinically into the far corner with the outside of his boot.
Graham Burke really should have made it 2-0 when he found himself freee just before the half hour as he got on the end of a fluid move but, fortunately for Dundalk, his downward header clipped Vemmelund's heel and somehow stopped dead in front of Rogers.
Burke had another chance to double the lead ten minutes from the break but, as he pulled the trigger, he was dispossessed by a wonderfully-timed challenge from Paddy Barrett.
The former Aston Villa man was involved in the second goal moments later, however, as his right-wing corner sailed over Rogers to McAllister at the back post, who had a free header into the corner.
The visitors belatedly rallied as the half drew to a close, and Massey forced a save from Chencinski with a first-time shot from just inside the area, but it was no trouble to the Canadian.
Dundalk offered little after the break as they had a lot of possession but found it difficult to build up any sustained play outside of their own half, the Rovers pressing stilting their passing game.
John Mountney created a chance from very little just before the hour as he beat Luke Byrne wide on the right and fizzed a ball across goal that evaded everyone, including the Dundalk attackers.
The Lilywhites' discipline deserted them in the final quarter. Hoare was booked for a wild lunge on Madden while Barrett saw yellow after confronting Finn when the Rovers captain fell under a challenge from Mountney.
Darren Meenan was sent off for a dive in injury time, and from Duffy's free kick Vemmelund sent a looping header over Chencinski to give Dundalk some hope.
There was to be no heroic fightback, however, as, on a bitterly cold night in Tallaght, the Lilywhites limped away a shadow of the side of the recent past.
Shamrock Rovers: Tomer Chencinski; Simon Madden, David Webster, Roberto Lopes, Luke Byrne; David McAllister (Sam Bone 89), Ronan Finn, Darren Meenan, Trevor Clarke; Graham Burke (Brandon Miele 80), Gary Shaw (Sean Boyd 80).
Dundalk: Gary Rogers; Paddy Barrett, Niclas Vemmelund, Sean Hoare, Dane Massey; Stephen O'Donnell (Chris Shields 32), Conor Clifford (Ciaran Kilduff 71), Patrick McEleney, Michael Duffy, John Mountney; David McMillan (Thomas Stewart 81).
