Adam Lallana came off the bench to score the winner as Southampton progressed to the fourth round of the Carling Cup by beating Preston.
Jos Hooiveld had put Saints in front with a first-half header.
Adam Barton levelled for Preston after the restart when he pounced on a loose ball after Bartosz Bialkowski failed to hold a Darel Russell shot.
But Lallana stooped to convert a Lee Holmes cross to seal a deserved victory for the Championship leaders.
The home side made 10 changes to their starting line-up following the weekend's impressive 4-1 demolition of Birmingham in the league.
It was one of the new faces, teenage academy product Ben Reeves, who made the opener, flicking on a corner to provide Dutch defender Hooiveld with a straightforward header.
The Saints dominated for large spells, and it was against the run of play when Preston scrambled an equaliser in the second half.
Goalkeeper Bialkowski failed to deal with a Russell effort from outside the box, and the enterprising Barton was on hand to steer the rebound home.
But Lallana's header, two minutes after coming on for Steve de Ridder, sealed the result for Southampton. The versatile midfielder started and finished a slick move, nodding a pinpoint cross past Preston keeper Andreas Arestidou after 66 minutes.
Preston boss Phil Brown, who himself had made 10 changes to his side, threw on in-form forward Neil Mellor with 10 minutes to go in a desperate attempt to create a goal and force extra time.
However the former Liverpool striker was unable to create an opening as Southampton closed out the tie.