Cork City centre back Derek Coughlan fired home his fourth goal of the season when he scored the winner at Turner's Cross yesterday.
Coughlan scored just on half-time when he pounced on a loose ball in the penalty area.
Cork did well to win a match that found them in less than compelling form.
"Derry are always a difficult side to play against and we are very happy to have taken three points," said a relieved Cork manager, Dave Barry. Derry's goal was created by Liam Coyle, and his whose cross from the left wing was headed home by Gary Beckett in the 33rd minute.
Cork's equaliser came after 38 minutes and after Coughlan had sent them in at halftime in front they saw Derry's final hopes evaporate when Derry's Paul Hegarty was sent off for a second bookable offence five minutes from time.
Cork City: Mooney, Daly, Coughlan, Hill, Cronin, Flanagan, Freyne, Herrick, Cahill, Dobbs, Kabia.
Derry City: O'Dowd, McCallion, Gauld, Curran, Kelly, (McCaul 77 mins)G O'Dowd, (R Coyle 56) Hegarty, Beckett, Hargan, L Coyle, McHugh.
Referee: J O'Neill (Waterford).