Harps looked like they might have secured a draw and snatched what would have been the first points for new managerial combo of Peter Hutton and Felix Healy.
But seven minutes from normal time, the Galway side popped up to snatch all three points thanks to a Tom King goal in the 83rd minute.
Indeed it was King who opened the scoring in the 36th minute for Mervue at Fahy’s field.
However Harps continued to battle bravely and were rewarded with a 55th minute equaliser by Marc Brolly.
However with the game looking like ending in stalemate, King proved he had the royal touch when he netted in the 83rd minute.
The strength in dept of the Donegal side’s squad is now beginning to tell as the first series of games comes to a close – one which the Finnsiders will want to forget as quickly as possible.
Manager Peter Hutton has admitted his young side are vastly inexperienced.
The return to the side of the likes of Conor O’Grady and Gareth Harkin cannot come quick enough.