Reporting by Matt Keane.
Patrick Hoban had two good chances to score for the visitors during the opening 45 minutes, but it was the second half before he was able to pick up his 27th league goal of the season.
He rose unmarked to head home a right-side cross from Sean Gannon.
Ronan Murray made it 2-0 just minutes later.
Dundalk almost had a third goal on 80 minutes, but Waterford’s Rory Feely cleared a John Mountney effort off the line.
Blues’ sub Dessie Hutchinson pulled a goal back with just a minute of normal time left to play to leave it 2-1 at the full time whistle.
It finished Waterford FC 1 Dundalk FC 2