Sligo Rovers lost their first Ford FAI Cup tie since November 2009 on Friday night after Monaghan United came away with a sensational 3-1 win at the Showgrounds.
Mark Quigley's ninth minute penalty look to have sent Rovers on their way, but goals from Tony Griffiths, Jason Marks and a Keith Quinn penalty sent Roddy Collins side into the next round of the Cup.
Sligo also had Alan Keane dismissed in the 77 minute for an off-the-ball incident.
Sligo were without Joseph Ndo (hamstring), Iarfhliath Davoren (calf) and Romuald Boco (international duty), but both Ross Gaynor and Gavin Peers returned to the starting XI after both players missed Monday night's defeat to UCD.
Sixteen-year-old Jake Dykes made his first senior start for Sligo in place of Davoren.
Monaghan boss Roddy Collins had to plan without John Reilly, Aidan Collins, Gareth O’Connor, Shaun Maher and Robert Bayly, while man of the match Alan Byrne was recalled to the first eleven.
Sligo, defending their FAI Ford Cup trophy for a second successive year, started the brighter and had the ball in the net as early as the second minute.
Alan Keane's cross dropped at the foot of Danny North, but linesman Damien McGrath judged to the ball to have crossed the touchline before North made contact.
Sligo's Lee Lynch saw his low shot come off the legs of Monaghan keeper Michael Schlingermann with seven minutes on the clock. North let Ross Gaynor's searching cross run across his body and to Lynch, before Schlingermann deflected the former Drogheda man's low drive on to the woodwork.
Sligo began to take control and went ahead with nine minutes on the clock when Stephen Maher took Gaynor down just inside the United penalty area. Mark Quigley sent the ball high and right and into the Mons net.
The away side had their first chance of note on 19 minutes when Conor Murphy's glancing header sailed in front of the Sligo goal, with Rogers looking beaten.
Monaghan had reason to celebrate ten minutes later, as Tony Griffiths sent a curling shot past Rogers from just inside the box after Maher set him up with a short pass to level the tie at half-time.
Jason McGuinness had a chance to put Rovers back in the lead on 52 minutes when he met another Gaynor corner with his forehead, but the former Bohs man was guilty of blazing the ball over the bar when unmarked.
Monaghan took the lead against the run of play on 72 minutes when substitute Jason Marks' cross from the left took a wicked spin and wrong-footed Gary Rogers, with the ball ending up in the corner of the Sligo net.
Five minutes later things went from bad to worse for Rovers as Alan Keane was sent off after an off-the-ball incident with a United player.
If that didn't frustrate manager Ian Baraclough enough, Danny Ventre tripped Willo McDonagh inside the Sligo penalty area with seven minutes to go. Keith Quinn stepped up and sent the ball past Rogers to round off a famous night for the Gortakeegan outfit.
Sligo Rovers: Gary Rogers, Alan Keane, Gavin Peers, Jason McGuinness, Jake Dykes, Lee Lynch, David Cawley, Danny Ventre, Ross Gaynor, Mark Qiugley, Danny North.
Subs: Richard Brush, Martin Owens, Pascal Millien (for Dykes 62), John Dillon, Liam Martin, Mark McGoldrick, Raffaele Cretaro (for Lynch 75).
Monaghan United: Michael Schlingermann, Paul Whelan, Stephen Maher, Conor McMahon, Alan Byrne, Conor Murphy, Keith Quinn, Wilo McDonagh, Shane Dunne, Tony Griffiths, Daragh Reynor.
Subs: Chris Bennion, Roddy Collins, Michael Isichei (for Whelan 68), Bobby Ryan (for Murphy HT), Jason Marks (for Dunne 57).
