Drogheda will go into the mid-season break holding the bragging rights in Louth after Paul Crowley's 65th minute header saw off Dundalk at Oriel Park.
Peter Hynes saw an early 30-yard drive crash against the bar for the Drogs, before Marc Griffin saw a wicked free-kick fly just wide of the hosts in the 14th minute.
The visitors took the lead in the 43rd minute when Eric Foley's quick free found Declan O'Brien. He shifted the ball for Ryan Brennan to cross and when O'Brien flicked the ball on, Sean Brennan was at the back post to cooly finish.
Dundalk levelled in the 63rd minute, with John Mountney's pull- back inch perfect for sub Gary Shanahan to fire home.
Drogheda restored their lead two minutes later. Foley sent in a brilliant cross and Crowley made no mistake.
Dundalk threw everything into attack, but Gabriel Sava made three wonderful stops late on.
Drogheda played the last five minutes of stoppage time with ten men after Foley saw red for a second bookable offence.
DUNDALK -- Cherrie; McLaughlin (McSorley 75), Foran, Burns, Murphy; Walsh, Shields, Mountney, McDonnell (Thomas 83); Griffin, O'Neill ( Shanahan 58).
DROGHEDA UNITED -- Sava; Quigley, Prendergast, McNally, Hand; R Brennan (Marshal 89), Crowley, Foley, S Brennan; Hynes (Breen 90), D O'Brien (M O'Brien 90).
REF -- P Tuite (Dublin).