Shane Long scored Southampton’s winner as the visitors maintained their impressive form of late with a 1-0 win at the Liberty Stadium on Saturday.
The in-form Saints had won four and drawn one of their previous five games and Long’s 69th-minute header fired them into the top six as Swansea lost for the first time under Francesco Guidolin.
Swansea were accommodating hosts as they created little of note, but they were left to rue referee Jonathan Moss’ decision not to award a penalty in the final minute when Saints substitute Maya Yoshida tangled with Alberto Paloschi.
Southampton were full value for their victory and Fraser Forster, for the sixth successive game since returning from a serious knee injury, kept a clean sheet to go past the 500-minute mark without conceding.
The game’s decisive moment arrived in the final quarter when Long, finding space in between defenders, was granted the freedom of the penalty area to convert James Ward-Prowse’s cross for his ninth goal of the season.
Even then, Lukasz Fabianski might have kept the ball out of his net but he fumbled it over the line to end Swansea’s unbeaten run at four games.
Southampton might have had a case for already being ahead as Graziano Pelle had seen his 57th-minute effort disallowed for Jose Fonte dislodging the ball from Fabianski’s grasp.
It was a close call whether Fabianski had complete control of the ball but he was relieved to see Moss intervene after Pelle stabbed the ball home.
Both teams came into the game on the back of good form, but it was Southampton who settled quickly and looked the more confident side.
Pelle’s volley forced Fabianski into a goal-line stop and Oriol Romeu and Ryan Bertrand could not control their shots from distance.
Swansea tried to get both their full-backs, Angel Rangel and Neil Taylor, forward but Southampton were able to smother home attacks at source by employing a successful high press.
Andre Ayew brought a comfortable save from Forster but the first period had reached its final minute when the Saints goal was genuinely threatened.
Paloschi helped on Rangel’s cross to the far post and Swansea would have wanted no-one other than Gylfi Sigurdsson to be on the end of it after scoring five goals in his previous six games.
But Sigurdsson blazed his volley over and Swansea were almost punished for the miss in the final attack of the half moments later.
Fernando Fernandez allowed Steven Davis’ cross to clear and Long was perfectly placed to open the scoring, but the Republic of Ireland international headed straight at Fabianski.
Swansea’s susceptibility in the air almost cost them from Bertrand’s second-half cross but Romeu got in the way of the lurking Pelle and his header was timid.
Pelle was then denied by Moss’ whistle and Southampton almost paid the price when Sigurdsson’s free-kick found Ashley Williams.
But the Swansea skipper could not provide the telling touch after getting goal side of Virgil van Dijk and a late flurry following Long’s strike failed to ease their relegation concerns.