This was Harps’ first game in the Premier Division since 2008. The aim this season is to stay up — and this was a great tonic on day one.
Derry nearly took the lead in the opening minute when Gareth McGlynn crossed deep into the box but Jordan Allan failed to connect properly with a header.
The visitors were clearly on top early on and McGynn then had an effort blocked while Aaron McEneff blazed a shot over from 20 yards.
City missed a golden opportunity to take the lead on 41 minutes when Allan headed a McGlynn corner over from close range.
Harps snatched the lead on the stroke of half-time when David Scully rose to connect with a left-wing cross and send the ball past a despairing Gerard Doherty.
Derry failed to really threaten Harps in the third quarter.
Harps then pounced with a second on 75 minutes with former Derry player Ryan Curran bursting though to score after the visitors lost possession near halfway.
Rory Patterson pulled one back on 90 minutes for City but Harps held on.
This was the 60th competitive meeting between the two sides since Derry entered the League of Ireland back in 1985 — with Harps having only won five times previously.
There was a minute’s applause before the start of the game in memory of the late Mark Farren, who hailed from Donegal, and who was a legend at Derry City. He passed away last month having lost a brave battle against cancer.
Gallagher; Coll, Cowan, Mailey, McNulty; Harkin, Molloy, Houston, Curran; Hanlon, Scully. Subs: McNamee for Houston (22 mins), Foy for Molly (77 mins), McHugh, Boyle, Flatley, McNamee, Funston, Brush.
Doherty; Vemmelund, McBride, Barry, Jarvis; McGlynn, McNamee, McCormack, McEniff; Allan, Patterson. Subs: Curtis for McGlynn (67 mins), Monaghan, Ward, Daniels, Boyle, Doherty.
Mr. T. Connolly (Dublin).