Finn Harps' Colm Deasy was shown a straight red card after his horrific challenge on Ciaran Coll.
The action packed five goal encounter at Ballybofey sparked into life on 37 minutes, as Harps were rightfully reduced to ten men when Deasy was shown a straight red card, for a terrible challenge on ex-Harps man Coll.
Derry broke the deadlock in the second half as Aidy Delap scored his first goal of season blasting home from close range on 53 minutes.
To their credit the ten men drew level on 75 minutes as Nathan Boyle scored against his old club, however things turned quickly back into City's favour thanks to Northern Ireland U21 striker David Parkhouse.
The front man gave Derry the lead again on 83 minutes when he powerfully headed home Jamie McDonagh's fantastic right wing cross.
Then in stoppage time a goalkeeping howler by Ciaran Gallagher allowed Parkhouse to sneak in and score.
The goalscoring wasn't over as Harps scored from the penalty spot on 95 minutes when substitute Mikey Place side footed home from the spot, after Ally Gilchrist was adjudged to have fouled Keith Cowan inside the box.