The Tractor Boys, who came into the game unbeaten in 11 matches, took a first-half lead at St Mary's when Darren Ambrose headed home but Morgan Schneiderlin capitalised on a defensive mix-up to put Saints level at the interval.
The hosts dominated the second period but failed to convert possession into chances as Ipswich earned another chance of progress with a dogged and determined display.
Southampton last reached an FA Cup final in 2003 when they were beaten 1-0 by Arsenal but Saints, sitting fourth in the Barclays Premier League, have realistic hopes of going one stage further this season, particularly as the traditional favourites' focus becomes diverted by European competition.
Ronald Koeman picked a near first-choice XI for the contest, with Schneiderlin returning from suspension, while Ipswich manager Mick McCarthy made six changes to his side, who are second in the Championship and gunning for automatic promotion.
Southampton dominated possession early on but Ipswich carved out the first clear-cut chance as David McGoldrick won possession on the right before cutting back for Stephen Hunt, who shot straight at Fraser Forster.
The visitors were causing problems down the flanks and in the 19th minute they made it count as Tyrone Mings drove to the line, chipped a cross into the penalty area where Ambrose had space to direct a looping header over Forster and into the net.
Mings, a reported transfer target for Arsenal, may have taken added satisfaction from his assist given he was released by Southampton aged 16 after being deemed too small.
Saints, however, responded immediately and should have been level when Dusan Tadic's through-ball sent Steven Davis clear, but the midfielder's side-foot finish was denied by the feet of Dean Gerken.
The home side continued to pile on the pressure and in the 33rd minute, Ipswich's resistance was broken as Gerken and Christophe Berra failed to clear a routine ball into the box and Schneiderlin nipped in to poke home the equaliser.
Saints maintained their ascendancy as the first period drew to a close although Ipswich midfielder Luke Hyam had Forster scrambling with a stinging long-range effort on the stroke of half-time.
The second half began much as the first had ended, with Southampton pressing forward and flooding the Ipswich box.
Shane Long thought he had a case for a penalty when he was taken down by Mings soon after the restart but referee Martin Atkinson was unmoved.
The home side continued to pin Ipswich back but struggled to create a decisive opening against their opponents' resolute defence.
Graziano Pelle, Jose Fonte and Ward-Prowse all saw shots blocked and 21-year-old substitute Lloyd Isgrove almost stole the show with a weaving run in injury-time but the teenager was unable to apply the finish.
Ipswich were desperately hacking the ball clear by the end as Southampton threw everyone forward in search of a winner but it was the away fans who were cheering at the whistle, with the prospect of a home replay to come.
Source : PA
Source: PA