Defeat sees Villa plunge further into trouble following a disappointing afternoon, but the Saints were fully deserving of their victory after producing a fine away performance.
Aston Villa controlled most of the opening period, with star striker Christian Benteke and Charles N’Zogbia looking lively in the early stages.
It was Benteke who created the game’s first chance six minutes in, when he curled an effort just over the bar from the edge of the area.
That proved to be the only real opportunity the home side enjoyed, and it was the visitors – who were always a danger on the counterattack – that made the better opportunities, Jay Rodriguez, Rickie Lambert and Luke Shaw all going close for Nigel Adkins’ side.
Southampton was promptly rewarded for its dominance just over 10 minutes before the interval as Lambert stepped up to convert from the penalty spot after Enda Stevens had felled Rodriguez just inside the area.
Villa offered little response and the Saints went close to doubling their lead minutes later when Luke Shaw strode past Matthew Lowton before seeing his powerful effort saved by Brad Guzan.
The hosts approached the second period with renewed energy and vigor, Lowton, Weimann and Benteke all having chances as Lambert’s men desperately searched for a leveller.
Still it was Southampton which always looked the more likely to score and again went close to adding a second when Jason Puncheon crashed an effort against the post.
The visitors did however suffer a blow when Shaw was stretchered off following a collision with Lowton, and that seemed to weaken the Saints defensively as Villa piled on the pressure in the closing stages.
First Benteke headed over from point-blank range, before Nathan Baker headed against the bar from a corner as the men from the south coast continued to ride their luck.
However, despite all of its possession and territory Lambert's side was not able to find a leveller as Southampton held on to earn a much-needed triumph.