A disastrous five minutes spell at the start of the second half wrecked Dundalk's hopes of a good result in their first premier league game of the season.
Up to that point, Dundalk had been playing at their best, with Peter Withnell back from honeymoon to give some bite to their attack.
Then, just five minutes into the second half, Marcus Hallows turned the game on its head, when he waltzed through a static Dundalk back four and pushed the ball under goalkeeper Steve Williams, for the lead goal for the visitors.
Just three minutes later, Hallows turned the screw with a great shot from the edge of the area, which Williams could only parry, and Conor O'Grady was in the right spot to push the ball to the net.
Worse was to follow for the home club as defender David Crawley, who had been booked in the first half, was shown a red card for dissent against a linesman's decision.
Dundalk still looked sharp at the re-start as David Ward shot narrowly wide five minutes into the period; but then, on the break, Sligo picked up that all important first goal and the game had been turned on its head.
After the Crawley sending off, the game became a little scrappy with no fewer than seven players, five from Dundalk and two from Sligo, booked.
Withnell had the best chance of pulling one back for Dundalk with about 15 minutes to go; but with all the time in the world shot just wide of the post.
DUNDALK: Williams, McNulty, Crawley, Doohan, Brady, Melvin, Campbell, Ward, Hoey, Withnell, Thew. SLIGO ROVERS: Boswell, Callaghan, Lynch, O'Grady, Birks, Sheridan, Jones, Moran, Hallows, Hetherton, Hutchinson. Sub: Shannon for Moran (11 mins).
Referee: A Carroll (Kildare)
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