The Republic of Ireland international curled in a free-kick to help Liam Buckley's side reach the quarter-finals of the Leinster Senior Cup
New Lilywhites forward David McMillan had the first proper chance of the game after some solid work in midfield from Richie Towell, but the former UCD and Sligo Rovers man was denied by Brendan Clarke in the home goal. Both teams cancelled each other for most of the first-half, with Clarke the busier of the two goalkeepers, saving from both Daryl Horgan and McMillan.
Chris Forrester had St Pat's best chance of the half as the clock wound down, but could not direct his effort on target. The midfielder went close again after the restart as the hosts began to take control of the game, but saw Peter Cherrie deflect his shot to safety.
Much to the delight of the home fans, Fahey found the net with a free-kick just after the hour mark. The Republic of Ireland international opened the scoring with a well-taken set-piece which clipped the bar on the way in.
Pat's lead didn't last long as McMillan was rewarded for his work up front with an equaliser after Kurtis Byrne put him through. However, the hosts restored their advantage with 20 minutes remaining thanks to a strike from Daryl Kavanagh.
Liam Buckley introduced new signing Conor McCormack to help hold onto the lead, keeping Dundalk at bay to win 2-1 and progress to the last eight of the Leinster Senior Cup.