Jannik Vestergaard opened the scoring with a powerful head to give Southampton a deserved lead after the visitors had an early goal called back for offside.
Che Adams, who entered full of confidence in front of goal, hit the back of the net inside three minutes, but was deemed offside in the build-up.
But Vestergaard nudged Saints ahead when he rose highest to meet Ward-Prowse’s free-kick delivery to direct a header across goal on 20 minutes.
Douglas Luiz then set up Southampton in a dangerous position when he gave away a free-kick on the edge of the box, allowing Ward-Prowse to step up and thrash a right-footed effort up and over the wall take make it 2-0.
Ward-Prowse then added a second tally to go along with his earlier assist with another stunning free-kick from straight on.
Matthew Cash was lucky to only see a yellow card after using a high hand to deny Theo Walcott a one-on-one chance at goal, but Ward-Prowse ensured Southampton took advantage of the error with a curling free kick to make it 3-0 on the stroke of halftime.
Alex McCarthy had little to do in the opening half, but denied Trezeguet and Jack Grealish in quick succession prevent Villa finding a way back into the game eight minutes after the restart.
Danny Ings found his goal to make it all Saints at 4-0 with a strike from the left edge of the box giving Emiliano Martinez no chance to stop the attempt.
Tyrone Mings pulled one back shortly after the hour mark, before Ollie Watkins and Grealish each added goals in stoppage time to set up a nervy finish for Saints.
But the full-time whistle and a fourth-straight win over Villa confirmed that Southampton climbed into third place in the table on 13 points from seven games ahead of the afternoon fixtures.
Aston Villa (4-2-3-1): Martinez; Targett, Mings, Konsa, Cash (El Mohamady 67); Douglas Luiz, McGinn; Grealish, Barkley, Traore (Trezeguet 29); Watkins
Unused subs: Steer (GK), Hourihane, Engels, Nakamba, Davis
Goals: Mings (62), Watkins (90+2), Grealish (90+5)
Bookings: Cash (43)
Southampton (4-4-2): McCarthy; Bertrand (Diallo 79), Vestergaard, Bednarek (Stephens 46), Walker-Peters; Walcott, Romeu, Ward-Prowse, Armstrong; Adams, Ings (Long 85)
Unused subs: Forster (GK), Stephens, Redmond, Djenepo, N’Lundulu
Goals: Vestergaard (20), Ward-Prowse (33, 45), Ings (58)
Bookings: Ward-Prowse (12), Diallo (90+2)