Although they had to play second fiddle to the visitors in the opening 10 minutes, once the outstanding Murdock let loose with two penalties either side of a blistering goal from Daniel Guinness the result was never in doubt.
Limerick’s Colum McSweeney was blackcarded for a foul on Liam Kerr and the home side went in at half-time 3-8 to 0-5 ahead.
It took Down 12 minutes to register their first score of the second half with Kerr firing over after Peter Nash tried to ignite fire in his side with a point of his own.
Pat Havern kept the scoreboard ticking over for Conor Laverty’s side with five points from placed balls as they eased to a fine victory.
Down scorers: O Murdock 2-3 (2-0p), P Havern 0-5 (5f), D Guinness 1-1, L Kerr 0-3 (1f), S Johnston 0-2, P Fegan, O Savage 0-1 each
Limerick scorers: P Nash 0-6 (4f), I Corbett, S Costello, C Fahy 0-1 each.