Mark Quigley put the home side ahead in the 10th minute and Gavin Peers doubled their advantage from a Ross Gaynor cross four minutes into the second half.
Substitute Liam Buchanan headed a Joseph Ndo corner past Peter Cherrie four minutes from time.
Dundalk came closest to scoring when Stephen McDonnell struck a post in the 64th minute. Solid defending by Dundalk cut out the danger as Mark Quigley teed up a shot in front of goal after four minutes of the first half.
The visitors goal had a let-off in the ninth minute when Raffaele Cretaro missed a crossed shot by Quigley but a minute later the Reds went in front when Quigley sent a sizzling low shot to the Dundalk net following a quick break out of defence by Rovers.
McGuinness had a headed effort cleared following a Ross Gaynor corner in the 19th minute as Sligo exerted pressure on the visitor’s defence.
Mark Griffin’s free kick from just outside the box after 31 minutes forced Sligo keeper Gary Rogers into a smart save. Substitute Pascal Millien was denied by a superb interception by Paul Whelan five minutes before half time.
The league leaders were dealt a double blow inside a five minute period in the first half when Alan Keane and striker Mark Quigley went off injured but the home side responded well taking the game to the visitors for the remainder of the half.
SLIGO ROVERS: Rogers, Keane, McGuinness, Peers, Ventre, Quigley, Cretaro, Gaynor, Ndo, Lynch, Conneely.
Subs: Millien for Keane 25, Buchanan for Quigley, 29.Cawley for Ventre, 83.
DUNDALK: Cherrie, Foran, Whelan, Burns, Shields, Rafter, Griffin, McDonnell, Maher, Shanahan, Murphy.
Subs: Walsh for Burns 52, Reilly for Shanahan, 72
Referee: T Connolly, Dublin.