After the highs of the FAI Cup quarter-final success midweek, Harps came back down to earth with a bump.
The home team got off to a great start and led 1-0 after six minutes through Jake Keegan who reacted fastest to pounce after Conor Winn coould only parry the ball.
But Harps improved and were the stronger side leading up to half-time.
Caoimhin Bonner went close for Harps just after the break but Vinny Faherty made it 2-0 to Galway on 56 minutes with questions being asked about the Harps' keeper who should have dealt better with a cross.
Galway sealed the issue just three minutes later with a great run by Ryan Connolly who crossed for the in-rushing Gary Shanahan to head home.
Harps used all three subs late on but Galway, roared on by the majority of fans in a crowd of just under 1,000, were never in danger of throwing things away.