Substitute Josh Daniels netted a deserved equaliser in the 83rd minute when sweeping Nathan Boyle’s low cross to the net to force a nervous finish.
Amazingly, the home side then took the lead in the 88th minute when Daniels found Rory Patterson who produced a magnificent finish and Harps were in difficulty.
However, as the clock ticked down, the Donegal side refused to give up and they sensationally levelled matters in the 90th minute when Sean Houston rose well to head the ball home to silence the home fans.
Making it even more interesting was Boyle’s miss when he poked the ball wide of the target from close range.
Derry had struggled to get to grips with the game from the outset, Harps forcing the issue without actually threatening the home goal.
And with the home lot struggling to get their passing and movement going, the visitors took full advantage scoring what appeared a very soft opening goal in the 20th minute.
Sean Houston rolled the ball into the path of Dave Scully and after his shot crashed off the Derry crossbar, Ryan Curran was first to react to break the deadlock.
The goal finally stung the “Candystripes” into action and five minutes after the goal, Barry McNamee wasted a glorious chance to level matters.
Patrick McClean floated a cross into the danger area when Patterson chested the ball into the path of the midfield but his shot was saved by Harps keeper Ciaran Gallagher.
In the 28th minute a superb pass by Keith Ward sent Patterson scampering into a one-on-one but the Derry striker failed to hit the target and another superb chance was lost.
Derry bossing the ball throughout the second period.
The home side really should have equalised in the 58th minute but Ward’s shot was blocked by Gallagher’s legs.
Gallagher saved again in the 69th minute, a powerful drive from Curtis parried wide.
And as Derry continued to push forward, no one could have expected that late, late drama.
Doherty; Vemmelund, McBride, Barry, McClean (Jarvis, h/t); McCormack, McEneff; Ward (Daniels, 77), B. McNamee, Curtis (N. Boyle, 77); Patterson.
Gallagher; McNulty, Cowan, Mailey, Coll; Molloy; Curran, Houston, T. McNamee (E. Boyle, 74); Hanlon; Scully.
Neil Doyle (Dublin).