The game was all but over at half-time as City were 3-0 by then – albeit with two of those goals in injury time before the break.
Barry Molloy gave the home side in the lead in the 37th minute and Harps would have been delighted to have gone in just a goal down.
But in the first minute of injury time Patrick McEleney fired City into a two-goal advantage – and a minute later Mark Farren’s effort (which did look off-side) made it 3-0.
Harps, believe it or not, had a good first half up until then.
Molly’s second goal in 87 minutes sealed a 4-0 win for City in front of just 800 fans at the Brandywell.
Derry City: Eugene Ferry; Simon Madden, Eddie McCallion, Ryan McBride, Matthew Crossan; Patrick McEleney, Barry Molloy, Owen Morrison ((Stephen McLaughlin 24) (Ryan Curran 72)), Brian McGroary; Mark Farren (Barry McNamee 74), David McDaid.
Subs not used: Gerard Doherty, Dermot McCaffery, Kevin Deery, Michael Barr.
Booked: Matthew Crossan (30)
Finn Harps: Shaun Patton; James Doherty (Hugh Carlin 73), Aaron O’Hagan, Thomas McMonagle, Ciaran Coll; Adam Clarke (Matt Harkin 54), Thomas McBride, Shaun McGowan, Paul Simon Tracey; Blain Curtis, Kevin McHugh (Barry O’Mahony, 47).
Subs not used: Ciaran Greene, Tommy Bonner, Paul McVeigh.
Booked: Thomas McBride (40).