Derry City's poor recent form continued, as Dundalk secured their second win of the season, at the Ryan McBride Brandywell Stadium.
Keith Ward's stunning first half strike was enough for Stephen O'Donnell's side to claim the points.
Derry's disappointing night was made worse as Sadou Diallo's first half red-card means the midfielder will miss next Sunday's Extra.ie FAI Cup Final against Shelbourne.
The visitors took the lead on nine minutes in stunning fashion as Ward's sublime strike on the half volley, from the right hand side of the penalty box, flew into Brian Maher's bottom right hand corner. City missed a golden chance to equalise on 19 minutes as Joe Thomson headed over from close range, after Daniel Lafferty's centre had picked out the midfielder.
Soon after both teams were reduced to ten men as referee Rob Hennessy sent-off Diallo and Robbie McCourt, after the pair clashed on the half-way line.
The Oriel Park men should have doubled their lead on 24 minutes as Ward played in David McMillan, but the striker's close range shot was saved by an out-rushing Maher. Moments later a clever pass by Brandon Kavanagh found James Akinrunde, but the striker's shot was well saved by the out-rushing Peter Cherrie.
Just before the half-time break Ronan Boyce's right wing cut-back found Thomson, but the in-rushing midfielder saw his tame strike easily saved by Cherrie. Derry were inches away from leveling things on 53 minutes, but Cameron Dummigan's long-range pile driver whistled just over Cherrie's crossbar. On 78 minutes Ryan Graydon's 20 yard strike failed to trouble Cherrie as he flew over the crossbar.
Derry missed a sitter to level things on 81 minutes as Patching found fellow substitute Jamie McGonigle but the striker blazed over with the goal at his mercy.
Derry City: Brian Maher, Ronan Boyce, Shane McEleney, Cameron McJannet, Daniel Lafferty (Ciaran Coll 72); Sadou Diallo, Cameron Dummigan, Joe Thomson (Jordan McEneff 82); Brandon Kavanagh (Will Patching 57), James Akintunde (Jamie McGonigle 72), Ryan Graydon.
Dundalk: Peter Cherrie, Lewis Macari, Brian Gartland (Andy Boyle 80), Darragh Leahy, Robbie McCourt; Alfie Lewis, John Martin (Ryan O'Kane 63), Joe Adams; Keith Ward (Stephen Bradley 71), David McMillan (Pat Hoban 71), Runar Hauge.
Referee: Rob Hennessy (Dublin).
