Owen Heary had spoken of getting back to normality following their European adventure, but the Shelbourne captain scarcely meant this. Derry arrived undaunted by the runaway league leaders.
Some early jitters in the Shelbourne defence helped to ease Derry into the match as they responded well to their FAI Cup semi-final defeat on Friday; Ciarán Martyn chipping just over having been gifted the ball by Jamie Harris.
Uncertainty remained in the home defence with goalkeeper Steve Williams clearing the ball straight to Gareth McGlynn whose shot wasn't far off target.
Shelbourne played only in fits and starts. Alan Moore twice shot wide from long-range free-kicks while Glen Fitzpatrick headed wide from a Jason Byrne cross, an omen of a 90 minutes in which the champions failed to get a shot on target.
Heary tried to inject some urgency, surging down the right to cross and set up Fitzpatrick. Damien Brennan kept his eye on the ball to make a vital block. It wasn't to get much better than that for Pat Fenlon's out-of-sorts side.
Shelbourne remained unsure in defence. David Crawley had to put his body in the way of a stinging shot from Alan Murphy after Clive Delaney headed down Killian Brennan's free-kick.
The impressive Brennan, making his first start, then brought the save of the half from Williams with a pacy left-footed free-kick on the stroke of half-time.
Having imposed themselves on a lethargic Shelbourne in the first half, Derry remained the better side into the second and finally took the lead on 57 minutes. On the pitch just a minute, Michael Holt won a corner. Killian Brennan added substance to his overall display with a good delivery and Peter Hutton's header beat Williams.
Holt then scored the clinching second goal on 76 minutes.
Crawley's overhit pass to Dave Rogers rebounded off his fellow defender to run kindly for Holt who showed languid composure to cut past Williams and shoot home.
SHELBOURNE: Williams; Heary, Harris, Rogers, Crawley; Moore (G McCarthy, 89 mins.), S Byrne (Cawley, 73 mins.), Crawford, Cahill; J Byrne, Fitzpatrick (Hoolahan, 60 mins.)
DERRY CITY: Forde; D Brennan, Delaney, Hutton, McCallion; McGlynn, Martyn, Doherty, K Brennan (Deery, 75 mins); Murphy (Holt, 56 mins), Beckett (O'Grady, 90 mins.).
Referee: I Stokes (Dublin).