James Akintunde scored on his debut before skipper Conor McCormack weighed in with a rare strike of his own to make it a job well done for Derry City.
The Candystripes had a point to prove after going down at home to Sligo Rovers on Friday, but gaffer Declan Devine was convinced his team would feel the benefits of new arrivals.
And while Adam Hammill, Jake Dunwoody and Ibrahim Meite must continue to quarantine, Akintunde is out the other side and was straight into the thick of it here at Richmond Park.
He set Derry on their way to a deserved victory after a streetwise performance against a Saints side that never looked threatening until Martin Rennie twice went close in injury-time.
Stephen O’Donnell’s charges were full value for their hard-earned point in Dundalk on Friday and may well have won. But they felt the effects of the quick turnaround and laboured throughout.
They saw plenty of the ball but did very little with it and while Robbie Benson carried an initial threat, their collective play lacked imagination. Derry had them sussed in that regard.
The Candystripes were no great shakes themselves in the final third although they had the better of the early half chances, but Brendan Clarke was comfortable.
So, too, was Peter Cherrie who kept out a Benson shot in the opening minutes. Clarke then mopped up from Gerardo Bruna while Jack Malone and Walter Figueira missed the target in quick succession.
Figueira should have atoned before the break but, with the Saints’ three-man defence scrambling, he didn’t react quickly enough in a good position inside the box. But Derry’s attitude was spot on and they duly got their rewards.
Four minutes into the second-half, raiding right-back Colm Horgan slipped in Jack Malone and his neat pass to Akintunde was turned home first time with Luke McNally closest to him but unable to react.
And the Saints’ woes continued thereafter. While sub Jason McClelland tested Cherrie after a Georgie Kelly layoff, the hosts’ issues in the final third continued to haunt them and Derry made hay.
Devine’s charges were hungrier in every department and skipper McCormack doubled the lead with 18 minutes to play.
Stephen Mallon chased down a lost cause, pressing McNally who was in possession at his own byline and the centre-back’s hacked clearance could only find Figueira 25 yards out. McCormack raced onto the ex-Chelsea man’s layoff and beat Clarke with a curling shot to the far corner.
ST PAT’S: Clarke; Feely, McNally, Desmond; Titov (McClelland 45), Lennon (Markey 75), Benson, Griffin; Ward (Forrester 52), Kelly (Rennie 63), Gibson (Burns 75).
DERRY CITY: Cherrie; Horgan, Toal, Gilchrist, Coll; McCormack, Bruna (Mallon 66), Malone (Clifford 89), Thomson, Figueira; Akintunde (Harkin 85)
Referee: R Hennessy
