Ollie Watkins and Douglas Luiz each had first-half tallies—with Saints fortunate to not be further behind at the break—before Philippe Coutinho and Danny Ings made it a comprehensive victory for Villa.
Southampton posed little threat on goal throughout the match and didn’t record a shot on target until Che Adams forced a save in the 57th minute, but the damage was already done.
Saints, who were without first-choice centre back Mohammed Salisu through injury, suffered their first negative result since a 3-1 defeat to Wolves on January 15.
Villa, meanwhile, picked up an important win in the race for a top-half finish with just two points separating ninth from 13th position.
The hosts made it 1-0 after just nine minutes when Ings played a perfectly weighted through ball to Watkins, who turned Jack Stephens inside out before firing beyond Fraser Forster.
Villa then had a chance to double their lead, but Jacob Ramsey headed well wide of the post with Ings making a similar run unmarked at the back post.
Watkins came close to adding to his earlier tally only for Forster to make a save with his foot after Coutinho played the forward into open space down the right side.
Saints were largely passengers in the opening half, but when they did finally create a chance, Adams headed over the bar from Tino Livramento’s cross.
Villa had a flurry of chances through Coutinho to push ahead further, but he fired wide of the far post before being deneid by Forster.
Douglas Luiz, however, made it 2-0 following sensational link-up play that saw Coutinho square the ball for a simple tap-in on 44 minutes.
Coutinho tried his luck again on the half-time whistle but dragged his shot inches wide after racing onto Watkin’s flick-on.
But the former Barcelona star finally found the scoresheet when he pounced on a blocked shot and threaded the ball through Forster’s legs to make it 3-0.
Ings turned from provided to goalscorer in the 54th minute when he connected first-time with Matthew Cash’s cut-back.
The road doesn’t get any easier with an in-form and re-tooled Newcastle visiting St Mary’s next Thursday.
Aston Villa (4-3-3): Martinez; Young, Mings, Chambers, Cash; Ramsey (Bailey 78), Luiz, McGinn; Coutinho (Buendia 81), Ings (Sanson 71), Watkins
Unused subs: Olsen (GK), Traore, Hause, Chrisene, Emeka Iroegbunam, O’Reilly
Goals: Watkins (9), Douglas Luiz (44), Coutinho (51), Ings (54)
Bookings: Watkins (75)
Southampton (4-4-2): Forster; Perraud (Walker-Peters 58), Stephens, Bednarek, Livramento; Elyounoussi (Valery 45), Romeu (Diallo 76), Ward-Prowse, S. Armstrong; Broja, Adams
Unused subs: Caballero (GK), A. Armstrong, Redmond, Djenepo, Smallbone, Walcott
Bookings: Romeu (69)