A delightfully contrived and executed second-half goal from Barry McNamee got Derry CIty back to winning ways and up to second place in the SSE Airtricity League Premier Division table as they flummoxed St Pat's at Richmond Park.
A third league defeat on the spin, and fifth of the season, leaves the Saints languishing in mid-table.
And though Liam Buckley side had a big shout for a late penalty, they can have few complaints as a terrific save from Brendan Clarke prevented Derry from winning by more.
Four points ahead of them in the table going into the match, Derry didn't lack for confidence as they settled the better with Sean Hoare getting an important block to concede the first corner of the night to the visitors from Rory Patterson's shot on ten minutes.
Neat improvisation from Derry's Keith Ward saw the winger chest up Ronan Curtis' cross to ping an overhead kick just over Clarke's bar.
Saints defender Hoare was policing dangerman Patterson well, a crunching tackle taking the ball off the striker's toe after Ward threaded it through to him on 23 minutes.
Four minutes later, a rehearsed corner saw Patterson lay off McNamee's corner for Conor McCormack to strike from distance, though it scarcely troubled Clarke.
Less direct, St Pat's were struggling to create much in front of goal, Birmingham having his shot deflected for a corner from Conan Byrne's cross their first real sight of goal on 29 minutes.
The serious defending was having to be done at the other end with Saints' skipper Ger O'Brien stretching to block Curtis shot out for a corner after Patterson set him up.
Saints' best chance of the first half arrived on 43 minutes. Byrne got through on goal from David Cawley's pass to toe wide while appearing to be of balance.
A minute later the Inchicore side had their first shot on target when Ger Doherty dealt ably with a low drive from Cawley.
Clarke made the first telling save of the night three minutes into the second half when getting down well to his right to parry away Patterson's shot after ward touched a free kick to him.
Derry then survived some Saints pressure before McNamee wasn't far off target with a fierce left-footer on the hour.
But the lively midfielder finally found the net to break the deadlock on 62 minutes.
A terrific one-two with Patterson lost Hoare and McNamee beat Clarke at his near post with a low left foot finish.
Clarke then prevented a second Derry goal on 74 minutes with a brilliant save to somehow deflect Patterson's shot over the top after the striker pounced on a mistake by Hoare.
Saints had a real call for a penalty on 82 minutes when O'Brien was knocked over by McClean.
Having consulted his assistant referee, Tomas Connolly gave the free outside the box.