A first-half penalty from Rickie Lambert was enough to give the visitors all three points and pile more misery on the Villans, despite a late rally from the hosts
A controversial penalty awarded for a foul on Jay Rodriguez separated the sides, with Rickie Lambert converting the spot-kick before the break.
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 – who made the better opportunities, Rodriguez, Lambert and Luke Shaw all going close for Nigel Adkins’ side.
Southampton were promptly rewarded for their 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 vigour, Lowton, Weimann and Benteke all having chances as Lambert’s men desperately searched for a leveller.
Still it was Southampton who always looked the more likely to score and they 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 Christian 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 their possession and territory, Lambert's side were not able to find a leveller as Southampton held on to earn a much-needed win.