Harps would have hoped to hold on for a point at this stage, but Derry were soon back in front when the impressive Mark Brolly fired home past Mailey to give the home side all three points.
This defeat was disappointing from a Harps perspective and with just three games remaining this season they will be hoping to propel themselves up the table out of the second last place they currently find themselves in.
Derry City : Eugene Ferry; Martin Doherty, John Carlin, Darragh McGee, Mark Hamilton; Ryan McGarvey, Patrick McDonald, Gareth Harkin, Mark Brolly; Gerard McLaughlin, Seamus Browne. Subs: Davy McLaughlin (for McGarvey).
Finn Harps: Liam Mailey; Glenn Rainey, Matthew Crossan, James Doherty, Shaun McGowan; Colm McGonigle, Cathal Sharkey, Darren Meenan, Gary Whoriskey; Davitt Walsh, Barry Mulligan. Subs: Alan Gethins (for Mulligan); Barry Tourish (for Walsh); Danny Keohane (for Whoriskey).
Referee: Paul Duddy