Airtricity League Premier Division: Dundalk 1-0 Derry City
Derry City's League of Ireland struggles continued as they suffered a hugely unlucky defeat against leaders and champions Dundalk at Oriel Park.
The Candystripes looked to be denied a clear penalty before John Mountney's deflected winner on 87 minutes.
Cillian Morrison seemed to be fouled by Paddy Barrett in the box on 65 minutes but referee Jim McKell didn't agree.
Mountney's shot deflected off Shane McEleney to beat young Derry keeper Shaun Patton with three minutes left.
It was extremely harsh on the Derry players and particularly Patton who had produced impressive handling all night after being called in to replace injured Gerard Doherty.
After after Mourtney's goal, Derry substitute Ryan Curran had a glorious chance to earn his side a deserved point but he delayed his shot and the ball was eventually cleared off the Dundalk line.
Patton's inclusion was one of four changes from last weekend's disappointing home defeat by Galway United as Peter Hutton attempted to arrest his team's poor run of form.
With Seamus Sharkey, Dean Jarvis and former Linfield man Seanan Clucas also handed starts, Derry produced a composed first-half display as they created more attacking attacking openings than the champions.
Whenever Dundalk did threaten, the superb Ryan McBride and his fellow defenders were able to thwart most of the attacks.
Granted, David McMillan did have an early chance for the home side after a short back pass by McEleney but the lively Morrison and Mark Timlin tested Dundalk keeper Gary Rogers before half-time.
Derry continued to frustrate Stephen Kenny's side in the third quarter before the match's big talking point arrived in the 65th minute.
The Derry players and management could not believe that referee McKell had deemed Barrett's challenge on Morrison to be fair.
Dundalk's first shot on target didn't come until the 74th minute as Patton tipped over a dipping Stephen O'Donnell effort from 25 yards.
The late onslaught that one would have expected from Dundalk didn't appear to be materialising but Derry suffered heartbreak three minutes from time as Mountney's effort beat Patton after good work from Richie Towell and McMillan.
As Derry chased an equaliser in the six minutes of injury time, Dundalk sub Kurtis Byrne wasted a glorious chance to make it 2-0 as Patton saved his weak effort.
Seconds later, Derry should have equalised but Curran delayed his shot with Sean Gannon's subsequent attempted clearance then having to be booted off the Dundalk line.
Derry's defeat was a sixth reverse in their opening 13 league games as they slipped to eighth in the 12-team table.
Dundalk's win extended their advantage over Cork City at the top to seven points.