Georgie Kelly hit a double to mercilessly down his home county team with his first goals for the Saints.
The striker, on loan from champions Dundalk, drilled home the opener on 14 minutes after great approach play by David Titov and Robbie Benson.
Kelly then punished a short back pass by Kosovar Sadiki to take the ball around keeper Mark McGinley and slide it into the net for his second on 27 minutes.
Having turned a Rory Feely’s header round the post moments earlier, McGinley denied Kelly (left) his hat-trick on 62 minutes when saving well with his body after Jay McClelland slid the forward through one-on-one.
The win edges St Pat’s up to fourth place in the Premier Division table overnight as Harps slumped to a fifth defeat on the bounce.
The sides meet again at Finn Park on Monday night in the first round of the FAI Cup.
