Derry City slipped to their first home defeat of the season as Dundalk secured a 2-0 win at the Brandywell.
The defending champions' superior quality in front of goal proved vital as Sean Murray's low finish and Patrick Hoban's penalty earned a narrow win.
Ally Gilchrist came closest to scoring for the Candystripes but his close-range effort flew over the crossbar.
Dundalk have moved up to second place in the Premier Division while Derry drop behind Cork City to fifth.
Declan Devine's side started their league campaign with home wins over UCD and Waterford and the hosts enjoyed a bright start on their return to the Brandywell after impressive away draws against Cork City and Bohemians.
Candystripes goalkeeper Peter Cherrie made amends for an early fumble with a diving save in the 24th minute to keep out Hoban's header from Dane Massey's cross.
At the other end, Dundalk's Gary Rogers also had to be alert to tip Barry McNamee's free kick over the bar and from the resulting corner Eoin Toal could not connect with his shot in the midst of a goal-mouth scramble.
The Lilywhite's extra quality began to tell as the game unfolded and the visitors took the lead when Michael Duffy got the better of Conor McDermott on the wing and his cross was diverted into the path of Murray, who stroked a low volley past Cherrie.
Derry might have been level before the break as Ciaron Harkin's long-range effort flew just over the bar before Gilchrist missed a glorious chance when he failed to keep his header on target from McNamee's corner.
Any optimism the Derry fans might have had at the break was crushed within minutes of the restart when Cherrie clattered into Hoban and injured himself in the process of conceding the penalty.
Replacement keeper Nathan Gartside's first involvement was to face Hoban but the striker made no mistake with his spot kick.
Substitute Dean Jarvis should have put the result beyond doubt in the 55th minute but he blazed his shot off target from Duffy's square pass.
Rogers again showed good reflexes to save a dipping free kick by Junior Ogedi-Uzokwe and another from McNamee and the visitors were able to see out the game, including seven minutes of extra time, without any further threat to their goal.
The Candystripes return to the Brandywell in two weeks time when they host Sligo Rovers on 29 March.