Champions Shamrock Rovers returned to winning ways in Ballybofey as Andy Lyons' double and a late Graham Burke penalty bagged the victory for Hoops, their first win in three.
As Ollie Horgan chews over the remnants of this defeat, with Drogheda United due at Finn Park on Monday, the Harps boss will rue how this one unravelled.
The game was already gone, with Lyons making it 2-0 with a neat finish in the 79th minute, when Mark Anthony McGinley, the Harps goalkeeper, took down Rory Gaffney who raced into the penalty area on a breakaway.
McGinley was sent off, meaning he’ll miss Monday’s game through suspension.
With Harps having used their full compliment of substitutions, Bastian Hery took the gloves as Burke - who had been denied four times by McGinley - stroked home the penalty.
Two minutes into added time at the end of the first half, Lyons wriggled free of the attention of the Harps defence at the near post head home from Jack Byrne’s corner.
McGinley thrice denied Burke in the opening 23 minutes.
Just three minutes in, Burke shot powerfully at McGinley from 20 yards after Ronan Finn's cross was only partially cleared by the hosts.
Midway through the half, Burke swivelled into position, but again fired too close to the 'keeper.
Moments earlier, McGinley parried away another testing drive from the Irish International.
It wasn’t all one-way traffic and Harps - who last September recorded a first win over the Hoops in 13 years - went closest of either side before Lyons’ opener.
Elie N’Zeyi, Harps’ French midfielder could scarcely believe the time afford as he took possession just outside the Rovers penalty area in the 11th minute.
N’Zeyi took aim, but his effort flew back off the inside of Alan Mannus’ left-hand post and into the arms of the grateful Rovers goalkeeper.
On the hour, Mannus tipped onto the crossbar when Ethan Boyle connected with a Rob Slevin cross.
Eric McWoods almost levelled the scores in the 67th minute. After outmuscling Lee Grace, McWoods rolled inches wide of the far post.
McGinley turned a Burke free kick around his post, but Lyons soon doubled the lead, clipping delightfully after combining with Gaffney.
Finn Harps: Mark Anthony McGinley; José Carrillo (Mark Timlin 77), Conor Tourish, Dave Webster, Ethan Boyle; Élie N'Zeyi, Erol Alkan (Rob Slevin half-time); Ryan Rainey (Yoyo Mahdy 35), Barry McNamee (Luke Rudden 80), Filip Mihaljević; Eric McWoods (Bastien Hery 77).
Shamrock Rovers: Alan Mannus; Sean Hoare, Roberto Lopes, Lee Grace (Sean Gannon 68); Ronan Finn, Gary O’Neill, Jack Byrne, Graham Burke (Sean Kavanagh 87), Andy Lyons; Richie Towell (Aaron Greene 87), Rory Gaffney (Aidomo Emakhu 87).
Referee: Rob Harvey.