In England for seven years, the 32-year-old striker netted the only goal of the game in the 13th minute, but that strike gave the Leesiders something to hold onto as Derry began to throw caution to the wind.
In fact, the Candystripes did finish the game stronger, but Cork defended resolutely to record their third win over Derry this season.
Cork remain four points adrift of league leaders Dundalk.
Derry started very well and with Rory Patterson suspended, Patrick McEleney led the front line with authority for the home lot.
Michael Duffy and Danny Ventre managed to get shots on target during the early stages but keeper, Mark McNulty, was not seriously troubled.
However, it was Cork City who broke the deadlock in the 13th minute, with a well worked goal, to stun a crowd of just over 2,000.
Following a Dan Murray clearance from defence, Mark O’Sullivan chested the ball into the path of Josh O’Shea on the left wing and having got to the end-line, O’Shea’s teasing cross was met by John O’Flynn.
O’Flynn displayed his predatory instincts getting to the ball first to produce a superb finish with his right foot
That goal stunned the home side and while Derry did manage to threaten, they found the Cork City defence in no mood to grant any favours, two solid banks of four limiting the space in the final third.
In fact, Cork continued to push on and in the 21st minute O’Flynn got another shot on target after Derry defender, Dean Jarvis lost his footing but keeper, Gerard Doherty, parried the ball wide.
Two minutes later Cork were under pressure when Derry put together a fine flowing move but when the ball was played into the path of Patrick McEleney, he failed to get the power into his shot and Brian Lenihan whipped the ball to safety.
In the 26th minute, Derry forced their way forward and when Barry McNamee played Jarvis in, his shot was blocked by Mark McNulty.
Stephen Dooley was next to try his luck in the 34th minute but again the Cork City keeper was well placed to deal with the shot.
The home side continued to pressurise and when McEleney was set up by Dooley, his right foot shot screamed over the bar from 18 yards.
With O’Flynn failing to reappear for the second half, possibly having taken a knock, Derry continued to battle their way back into the game and in the 64th minute should have levelled.
McEleney played the perfect pass into the path of new signing, Shaun Kelly, but the full-back blasted the ball into the side netting.
McNulty pulled off a sensational save in the 79th minute touching McEleney’s dipping free-kick over his crossbar.
Cork substitute Danny Morrissey then crashed a shot wide having weaved his way into the box.
McEleney set up Dooley in the 86th minute but his header was easily while Mark Timlin’s shot skimmed off the crossbar in the 89th minute.
Cork held on and got their reward to the delight of their travelling support of 200 fans.
DERRY CITY: Doherty; Kelly (Boyle, 74), Byrne, Barry, Jarvis (Timlin, 80); Ventre (Curran, 90), McNamee; Dooley, Lowry, Duffy; McEleney.
CORK CITY: McNulty; Lenihan, Muirray, Dennehy, Gaynor; Dunleavy, G. Morrissey; O’Shea (McSweeney, 80), Kearney (D. Morrissey, 66), O’Flynn (Kavanagh, h/t); O’Sullivan.
Referee: Mr D. Tomney (Dublin).