Darren Ambrose netted the first goal of his third spell with the Blues before Morgan Schneiderlin equalised with Town drawing 1-1 at Southampton at half-time in their third round FA Cup tie.
Mick McCarthy made six changes to the team which beat Charlton 3-0 on Tuesday with Ambrose handed the first start of his third spell with the Blues.
Kevin Bru, Stephen Hunt, Dean Gerken, former Saints academy schoolboy Tyrone Mings and Luke Hyam came into the team for Cole Skuse, former Southampton keeper Bartosz Bialkowski and Jonny Parr, who dropped to the bench, while Teddy Bishop, Jay Tabb and Paul Anderson were left out of the 18.
Cameron Stewart was named on the bench for the first time since joining the club in the summer.
The Blues, who took an away following of 5,500 to St Mary's, a record at the Saints' current home, started in a 4-4-2 formation with Hunt and Ambrose in the left and right wide midfield roles respectively.
Former Town keeper Kelvin Davis is on the bench for the home side, who made only two changes from the team which beat Arsenal 2-0 on New Year’s Day.
The Premier League side played keep-ball for the first five minutes but without threatening Gerken’s goal.
On eight Bru scraped a low shot well wide of England keeper Fraser Forster’s right post from the edge of the box, the first chance of note at either end.
The Saints continued to dominate possession but without creating a significant opening, although Victor Wanyama wasn’t too far away from Gerken’s right post with a powerful 30-yard strike in the 14th minute.
Almost immediately, Town carved out a decent chance at the other end, McGoldrick seizing on a loose pass on on the Blues right and cutting a low ball back to Hunt on the penalty spot, but the Irishman’s shot was straight at Forster.
There was a scare for the Saints in the 17th minute when skipper Jose Fonte air-kicked Gerken’s long clearance but Forster was on to it ahead of Murphy. At the other end, Hyam blocked from Wanyama on the edge of the box.
The Blues had been increasingly getting a foothold in the game and in the 20th minute they went in front.
Murphy’s clever ball sent Mings away in space on the left, the full-back crossed from the byline and Ambrose looped a header beyond Forster and into the top corner of the net to send the 5,500 at the other end wild. It was the 30-year-old midfielder’s first Blues goal since February 2003.
Graziano Pelle wasn’t too far away for the Premier League side on 24, the Italian striker flicking Ryan Bertrand’s low cross from the left beyond the far post.
The home side went close again a minute later when Dusan Tadic played in Steven Davis one-on-one with Gerken, who came off his line to save with his foot. Tommy Smith blocked the rebound from Pelle.
Despite those chances, it was by no means all Southampton. On 28 Bru fed Murphy in space on the right of the area and his cross was only just behind McGoldrick, Fonte clearing.
Gerken got down well to his right to save James Ward-Prowse’s 25-yard freekick on 29, then a minute later Morgan Schneiderlin was booked for a foul on Ambrose. Christophe Berra joined him in referee Martin Atkinson’s book soon afterwards.
The Saints got back on terms in the 33rd minute via a goal Berra and Gerken will want to forget. The Scottish international defender was trying to shield a loose bouncing ball back to his keeper, who he was expecting to come off his line rather quicker than he was, and Schneiderlin stuck a leg in between them to divert it into the net.
The Town goal came under siege following the equaliser with goalscorer Schneiderlin amongst those having efforts blocked.
On 38 the Blues broke quickly, Murphy feeding McGoldrick to his left, but the Town number 10 chipped over.
Bertrand saw a volley deflect wide on 40 with the game still being played mainly in and around the Town box.
Moments before the end of a thoroughly entertaining half, Hyam unleashed a rocket from 30 yards which appeared to catch a defender on its way past Forster’s right post.
Town had been by no means outclassed by their Premier League opponents, creating a number of opportunities in addition to the goal, despite the Saints having enjoyed much the greater share of the possession.
Ambrose showed the goalscoring instinct Blues supporters will remember from his first spell at the club, finishing the well-worked move down the left with a superb header.
While the Saints’ goal was down to a mix-up between Berra and Gerken, on the balance of the game the home side didn’t deserve to be behind at the break.
Southampton: Forster, Ward-Prowse, Fonte (c), Gardos, Bertrand, Wanyama, Schneiderlin, S Davis, Tadić, Long, Pellè. Subs: Davis, Alderweireld, Isgrove, Reed, McCarthy, Targett, Seager.
Town: Gerken, Chambers (c), Mings, Berra, Smith, Hyam, Ambrose, Bru, Hunt, Murphy, McGoldrick. Subs: Bialkowski, Parr, Stewart, Skuse, Bajner, Clarke, Sammon. Referee: Martin Atkinson (West Yorkshire).