Mark Timlin rolled a stray pass across the six yard box into the path of Rory Gaffney who made no mistake steering the ball home.
The first half was poor and had that end of season mid table safety feel about it.
Things improved after the break. Shane Duggan opened the scoring for Limerick on 58 minutes.
Barry Mc Namee equalised on 53 minutes.
Rory Patterson nearly levelled in injury time but saw his shot hit the side net.
Dundalk remain just ahead of Cork City in the battle for the honours at the top of the Premier Division.
Dundalk recovered from being held scoreless during the opening-half to beat basement side Athlone Town by 3 goals to nil, with Pat Hoban scoring twice for the Lilywhites.
Cork remain just behind the leaders on goal difference after they ran-out 4-nil winners over UCD.
Garry Buckley scored twice for the Leesiders in the second-half after goals from Ross Gaynor and Billy Dennehy had put them in control by half-time.