Jake Hyland capped a superb performance at the heart of the Drogheda midfield with a goal as Pete Mahon's men made it two from two in the league.
United continued their unbeaten start to the season with a confident performance as Hyland's 65th-minute opener and Pat Cregg's injury-time own-goal condemned the struggling Saints to a second successive defeat.
Drogheda almost hit the front within six minutes when Stephen Dunne's shot was tipped onto the crossbar by Barry Murphy.
Sam Verdon went closest for Liam Buckley's men but his shot was blocked by Ciaran McGuigan.
Pat's were out of luck again shortly after the break when Billy Dennehy rattled the woodwork.
And they must have feared it wasn't going to be their night when centre-back Rory Feely's header was blocked on the line.
Hyland latched onto Gavin Brennan's through-ball and coolly finished for the opener before Cregg deflected in Colm Deasy's effort at the death.
DROGHEDA UTD - McGuinness; Deasy, Gallagher, McGuigan, Dunne; Purdy, Thornton (McEvoy 78), Hyland; Byrne (McCaffrey 70), Elliott (Griffin 79), G Brennan.
ST PAT'S - Murphy; Barker, Desmond, Feely, Bermingham; Cregg, Dennehy (K Byrne 85), Kelly, Verdon (J O'Hanlon 68), A O'Hanlon (C Byrne 68); Fagan.
Ref - S Grant (Wexford)