Romain Perraud scored either side of half-time as Southampton survived a fightback by Championship strugglers Blackpool to reach the FA Cup fifth round.
Perraud, on set-piece duties in the absence of captain James Ward-Prowse, broke the deadlock with a thumping effort into the far corner midway through the first half.
The 25-year-old left-back doubled his and Saints' tally just after the hour mark, collecting Sekou Mara's return pass before finishing confidently past visiting goalkeeper Chris Maxwell.
Blackpool, playing their first game under new manager Mick McCarthy, twice went close to cancelling out Perraud's opener but Jerry Yates and Ian Poveda both failed to make the most of good opportunities.