Pablo Counago's goal set up a grandstand finish at St Mary's but it wasn't enough to keep Town in the cup.

The Spaniard slid the ball in from eight yards as the game went into added on time and Blues had chances to salvage a draw but goals from Wayne Thomas and Michail Antonio proved enough to take Saints into the Fifth Round.

Blues dictated much of the play in the first-half but went behind on the half hour when Thomas thundered in a terrific strike from 25 yards and Antonio's first touch after Rickie Lambert's free-kick tested Arran Lee-Barrett low down proved decisive.

Roy Keane made one change to the team that beat Coventry last week, Carlos Edwards returning to the side with David Norris dropping to the bench.

Town started brightly, Stern John winning a free-kick inside the first minute and Kelvin Davis beat out Grant Leadbitter's free-kick with his feet after the wall had failed to do its job.

Former Town 'keeper Davis was called into action moments later, bursting off his line to clear from Leadbitter.  Lambert failed to get any pace on his shot from 18 yards in Saints' first opening, new signing from Southend, Lee Barnard, also failing to trouble Arran Lee-Barrett in the Town goal.

Good link up play between Edwards and Liam Rosenior carved out a corner for Blues, Damien Delaney's header kept out by Davis as Blues edged the opening exchanges.

Jack Colback was inches away from getting on the end of Jon Walters' cross, Owen Garvan then threading a pass through for Colback whose cross beat everyone.

It was Saints that opened the scoring though just past the half hour mark. They hadn't troubled Lee-Barrett until then but the Blues 'keeper couldn't do anything to prevent Thomas' 25 yard strike hitting the net to give Alan Pardew's side the advantage.

Davis saved from Gareth McAuley as Town responded, the 'keeper doing well again to take Rosenior's cross on the line.

The half finished with Town dictating possession but failing to beat Davis, Jaime Peters' cross escaping Walters at the far post.

Blues made a change at the break with skipper Walters making way for  Counago, the Spaniard immediately in the action with the referee denying him a goal after judging that he had not touched a long throw before the ball went in the net. 

Tamas Priskin replaced John in a second change for Blues just before the hour mark, Counago booked for foul in midfield as Saints enjoyed a flurry of chances, Lambert heading over then Lee-Barrett punching clear from Barnard at the far post.

Edwards made way for Lee Martin for the last 25 minutes, Saints then introducing Antonio and Simon Gillett for Barnard and Lloyd James and it was Antonio who reacted quickest seconds later to extend his side's lead after Lee-Barrett had blocked Lambert's free-kick.

Priskin had a shot blocked as Town looked for a way back into the tie, the Hungarian international then heading wide from a corner while at the other end Antonio blasted over from the angle.

Lambert volleyed just over before Counago gave Town a lifeline as the game entered the five minutes of added on time but it wasn't enough to keep Town in the cup.

Southampton: Davis, Thomas, Perry, Jahdi, Mills, Lallana, James (Gillett 70), Wotton (Lancashire 87), Holmes, Lambert, Barnard (Antonio 70). Subs not used: Harding, N'Diaye, Saganowski, Bialkowski.

Town: Lee-Barrett, Rosenior, McAuley, Delaney, Peters, Edwards (Martin 65), Leadbitter, Garvan, Colback, Walters (Counago 46), John (Priskin 58). Subs not used: McLoughlin, D.Wright, Balkestein, Norris. Booked: Counago, Leadbitter.
Att: 20,446