Dundalk have suffered a 3-0 defeat to NK Celje, ending their Champions League campaign for the 2020/21 season.
The Lilywhites will now enter the Europa League qualifiers following their humbling loss to the Slovenian champions at the Ferenc Szusza Stadion in Hungary.
NK Celje took the lead through Luka Kerin two minutes before half time, before late goals from Dario Vizinger and Filip Dangubic secured the Slovenian champions' first win at this level.
Vizinger almost gave NK Celje, who won their Slovan Prva Liga title last month, the lead just shy of the quarter hour mark, curling an effort just wide of Gary Rogers' post.
At the other end, Dundalk defender Brian Gartland headed Stefan Colovic’s corner over the crossbar.
Michael Duffy tested goalkeeper Matjaž Rozman with two tame efforts; one a header, the other a shot from distance.
The breakthrough came in the 43rd minute, after Chris Shields' strong tackle in midfield inadvertently sent the ball back towards his own goal.
Gartland was caught on his heels, with Kerin nipping in behind him to go through against Rogers.
The forward was nudged to the ground by Gartland, but managed to hook the ball past Rogers - who should have done better - despite lying on the ground inside the box.
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The concession of the goal rattled Dundalk, who almost allowed NK Celje to double their lead before the interval. Rogers was forced to make a reactive save to keep out a Ivan Božić cross which took a dangerous deflection off Gartland.
Dundalk created plenty of chances in the second half, with Jordan Flores forcing Rozan to tip the ball over the crossbar with a powerful drive from the edge of the box.
Duffy flashed another effort narrowly wide a minute later, before Rogers was once again called into action to deny Vizinger at the other end of the pitch.
Vinny Perth turned to his bench for inspiration, introducing David McMillan, Sean Murray and Nathan Oduwa as the second half wore on.
The Lilywhites came agonizingly close to an equalizer in the 84th minute, with Patrick Hoban heading Duffy's deflected free on to the woodwork.
Dundalk never gave up, but fell further behind in the 89th minute after an error from defender Sean Hoare.
Hoare conceded possession far too easily, with his intercepted pass eventually being squared for the lively Vizinger to tap into an empty net from six yards.
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NK Celje capped off an historic night for the Slovenian club deep into stoppage time when Dangubic reacted quickly to tap home a third goal after Rogers' weak parry from a free kick from distance.
Celje will now take on Norwegian side Molde in the next round, with Dundalk's Europa League opponents yet to be confirmed.
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Pressure continues to mount on Dundalk manager Perth, with the reigning SSE Airtricity League champions also struggling domestically.
The Lilywhites are eight points behind league leaders Shamrock Rovers with just eight games remaining.
"I do believe in that group of players and I believe that at the very minimum they can get back in and qualify for Europe again," Perth said after Wednesday's defeat in Hungary.
"They still have a European campaign. It’s not over. They must learn from that but they will. I don’t fear for that group in that sense.
"We’ve got good players at Dundalk and an amazing squad with amazing people but they just need to be backed at the moment and I think they’ll be great again."