Derry City crashed out of the Extra.ie FAI Cup, as Tunde Owolabi's second half penalty was enough to secure Finn Harps' first ever cup success over their North West neighbours.
In a disappointing cup tie, Ollie Horgan's men just about shaded it to come out on top and in doing so secured their fifth victory on the bounce and kept their fourth clean-sheet during that impressive run.
City were poor throughout and never really tested former Brandywell fans favourite Gerard Doherty, who made a few routine saves after Owolabi's spot-kick.
The Brandywell men made one change to their side which defeated Sligo Rovers last week, with experienced midfielder Bastien Hery replacing Evan McLaughlin, who dropped to the bench.
As for the home side they made four changes to their team which impressively seen off St Patrick's Athletic last Friday night, with former City number one Doherty starting in goals, Shane McEleney, Johnny Dunleavy and Adam Foley also came into the starting line-up.
Neither side really got going in the opening 30 minutes as both teams were doing some shadow boxing and didn't really create an opening.
After all the hype leading into the tie about both Harps and Derry as the two in-form teams in the country, the opening 45 minutes was a dreadful tight affair.
Harps had to make a substitution just before the break with winger Karl O'Sullivan replaced left-back Jordan Mustoe, after the defender picked up an injury.
The Donegal men created a good half chance right on the stroke of half-time as Barry McNamee's right footed cross found Owolabi inside the box, his close range strike was blocked by Eoin Toal and Ryan Rainey's follow-up strike deflected off Jack Malone and while Harps claimed for a penalty, referee Rob Harvey waved away their claims.
Foley had the first real effort on goal in the second half, but his snap on 56 minutes from just inside the penalty box, fizzed just over Nathan Gartside's crossbar.
That man Foley went close to breaking the deadlock four minutes later when he had the first shot on target, after he did well to outmuscle Danny Lafferty, before his left footed 20 yard strike, was superbly tipped over by a diving Gartside.
Derry boss Ruaidhri Higgins made his first change on 65 minutes with James Akintunde replacing Hery, as the visitors tried to get some sort of foothold in the game and the home side had to make their second change themselves minutes later when Kosovar Sadiki replaced the injury Ethan Boyle.
The Donegal men were awarded a penalty on 73 minutes after Ronan Boyce fouled Rainey inside the box, when he attempted to clear his lines but instead caught the winger, referee Harvey pointed to the spot and Owolabi, who netted a hat-trick against St Pat's, made no mistake from the spot, firing high into Gartside's top right hand corner.
Harps had a golden chance to double their lead moments later as Foley's right wing cross found Rainey at the back post, but his close range header, which had Gartside beaten, flashed just wide.
Doherty had to make his first save on 82 minutes when he did well to get down low and parry away substitute Evan McLaughlin's 20 yard right footed drive.
In the closing stages Doherty parried two efforts away tipping Ciaran Coll's long range cross-cum-shot over the bar and diving to his right to push away Jamie McGonigle's long range strike, as the Candy Stripes tried in vain to take the tie into extra-time.
Finn Harps: Gerard Doherty, Ethan Boyle (Kosovar Sadiki 67), Shane McEleney, Dave Webster, Jordan Mustoe (Karl O'Sullivan 45); Johnny Dunleavy, Mark Coyle, Barry McNamee; Adam Foley, Tunde Owolabi (Sean Boyd 85), Ryan Rainey.
Derry City: Nathan Gartside, Ronan Boyce (Patrick Ferry 84), Eoin Toal, Ciaran Coll; Jack Malone, Ciaron Harkin (Evan McLaughlin 76), Bastien Hery (James Akintunde 65), Joe Thomson, Danny Lafferty; Junior Ogedi-Uzokwe, Jamie McGonigle.
Referee: Rob Harvey (Dublin).