Goals from Darius Vassell, Joey Barton and DaMarcus Beasley meant it was City as opposed to the Saints who go marching on.
Yet it wasn't a straight forward passage as George Burley's in-form Championship side had the audacity to take a first-half lead.
But it was only the briefest of advantages as City were back on level terms within three minutes and never looked back when Barton put them ahead in first-half stoppage time.
Indeed Saints, who came into the game unbeaten in eight league and cup matches, could have been beaten more heavily but for a number of decent late saves from keeper Kelvin Davis.
And the display from City was a perfect pick-me-up following a retched display in their previous game which ended in a 3-0 home defeat by Blackburn.
City made three changes following that loss as Bernardo Corradi and Stephen Jordan were dropped, while Trevor Sinclair was ruled out through suspension.
Barton returned after serving a one-match ban, while Georgios Samaras and Beasley won recalls to the starting line-up.
Only a smart save at the feet of Vassell by keeper Davis prevented City from taking an early lead.
But Saints came closest to snatching the lead in the 14th minute when David McGoldrick's 30-yard drive bounced in front of keeper Nicky Weaver who managed to get a hand to the ball and divert it over the crossbar.
Saints went ahead midway through the opening period and seconds after Samaras had come close to putting City ahead.
Davis threw the ball out to McGoldrick whose long forward pass caught out the City defence. Weaver raced out of his penalty area but Kenwyne Jones managed to get to the ball first and lob it into an empty net for his ninth goal of the season.
Saints' joy was short-lived as City were on level terms within three minutes when Hatem Trabelsi's low cross from the right found Vassell who found the net with a well-executed near post shot on the turn.
Vassell's goal lifted City who produced some dangerous attacking raids and were only denied further reward by some resolute Saints defending as they managed to keep City at bay.
But in the second minute of stoppage time at the end of the first half, City snatched the lead when Stephen Ireland burst from midfield and released Barton with a slide-rule pass and he produced a clinical finish from 12 yards.
Vassell made a dangerous break from his own half and released Samaras following a wonderful through ball only for the Greek striker's shot to be deflected by a defender for a corner when perhaps he ought to have done better.
Saints made a double substitution just after the hour-mark taking off right-back Alexander Ostlund and striker Grzegorz Rasiak and replacing them with Czech Republic player Mario Licka and former City striker Bradley Wright-Phillips.
They failed to turn the game the Saints' way and it was City who sealed victory with 20 minutes to go when Richard Dunne's long clearance released Beasley who rounded goalkeeper Davis on the edge of the penalty area and almost walked the ball into the net.
City ought to have added to their tally in the latter stages had Davis not made three decent saves. He twice denied Ireland and then at the death managed to foil substitute Ishmael Miller.