Dundalk have moved two points clear at the top of the SSE Airtricity Premier Division.
Stephen Kenny's side came from 1-0 down to win 4-1 at Derry City and inflict a first home defeat of the season upon the Candystripes.
Brian Gartland, Robbie Benson, Michael Duffy and Krisztian Adorjan got the goals for the Louth side after Darren Cole's opener.
Waterford stay third after a last-gasp Gary McCabe penalty secured a 2-2 draw for bottom-side Bray at the Carlisle Grounds.
Gavan Holohan and Courtney Duffus got the goals for Waterford after Daniel McKenna's third-minute opener.