Swansea City were made to rue their missed chances as a goal either side of half time from Southampton saw Mauricio Pochettino's side climb into the top four of the Premier League.
Pablo Osvaldo was the only man to come close in the first 10 minutes before the hosts made their early pressure pay in the 19th minute.
Steven Davis found the run of Adam Lallana, cutting in from the right, and the Saints skipper rifled a shot past Michel Vorm into the top corner.
Despite going ahead, Southampton were on the back foot for large parts of the first half as Swansea did everything but equalise before half time.
Artur Boruc kept out efforts from Michu, Jonjo Shelvey and Wilfried Bony, while Nathan Dyer beat the Polish goalkeeper but not the inside of the post in the 36th minute.
The end-to-end nature of the first 45 minutes calmed a little in the second half as Southampton slowed the pace down.
Victor Wanyama thought that he had doubled the hosts' advantage when he found the net from a corner, but referee Mike Dean blew for a foul.
Three points were sealed for the home side seven minutes from time when Jay Rodriguez pounced on some hesitancy from Chico Flores to fire home.
Southampton now have 14 points from their first seven games, while Swansea stay 14th on seven.
