Basking in the afterglow of their memorable 1-0 win against Manchester United, Saints arrived in Suffolk looking to avoid looking another cup exit to lower-level opposition.
The Premier League high flyers were last month embarrassed in the Capital One Cup quarter-finals by third-tier Sheffield United, but they did not slip up against the Championship promotion chasers as Shane Long's first-half strike saw them through 1-0 victors.
It was a far cry from the quick Ipswich start that had those inside a packed-out Portman Road crowd - and millions watching on terrestrial TV - believing an upset could be on the cards, with Stephen Hunt finding the net early on.
However, the veteran Town midfielder's effort was chalked off for offside and Mick McCarthy's promotion chasers managed just one other shot on Fraser Forster's goal.
Saints were pragmatic rather than pretty, though, with the decisive goal coming after 19 minutes when Long reacted quickly to produce a lovely finish after James Ward-Prowse was tackled.
The much-changed visitors failed to create many more clear-cut chances but were able to extend their unbeaten run in all competitions to seven games, setting up a fourth-round clash with former manager Alan Pardew and his Crystal Palace side.
The only negative on the night was the hamstring injury sustained by Victor Wanyama - a particular concern following the pre-match news that fellow defensive midfielder Morgan Schneiderlin faces up to three weeks out with an adductor strain.
The France international was one of five alterations to the win at United and perhaps those changes were behind the Premier League side's slow start - one which Ipswich thought they had capitalised on.
With less than five minutes on the clock, Hunt raced onto a Kevin Bru through ball and beat Forster, only for the offside flag to bring the Irishman's celebrations to a halt.
That let-off gave Saints' defence a jolt but those in front of them struggled to find any coherence, with a wayward Wanyama effort from distance all they could muster until the 19th minute.
Neat team play and a clever turn saw Ward-Prowse through on goal
Ipswich captain Luke Chambers produced a wonderful challenge to deny the England Under-21s midfielder, only for the ball to fall for Long to fire home an impressive first-time strike.
Wanyama and Ward-Prowse had efforts of differing quality from distance as they attempted to add to the opener, while Long twice bore down on former Southampton goalkeeper Bartosz Bialkowski.
Dusan Tadic saw a goalbound shot blocked as the first half entered stoppage time - a period in which the visitors key man Wanyama sustained a game-ending hamstring injury.
Things could have got even worse for Saints after their former striker David McGoldrick got free, but he could only fire into the side-netting.
Long continued to prove a nuisance when play resumed after half-time, when Town at last began to make an attacking imprint.
Substitute Tyrone Mings, another with Southampton links, provided a fine cross which Darren Ambrose directed goalwards - the Tractor Boys' only shot on target - while a dangerous cross from the bandaged Daryl Murphy called Jose Fonte into action
Ipswich were now enjoying more possession but too often the final ball let them down, with Saints skipper Fonte helping his team keep firm at the back.
As the clock wound down Bru failed to find the target, as did substitute Graziano Pelle at the other end, and Saints progressed.
Source : PA