A brace from Ashley Westwood was not enough to stop Villa falling to their 25th league defeat of the season.
Villa were behind after 15 minutes, when Shane Long was allowed to head past Brad Guzan after incredibly poor defending from Joleon Lescott had left him unmarked.
The visitors had their second when Dusan Tadic fired home after Bacuna had passed the ball to Long, who then dragged Guzan and Lescott wide before squaring it to Tadic who fired into an empty net.
Villa did get one back before half-time, after Ashley Westwood managed to get into the penalty area and poke the ball past Fraser Forster.
Kevin Toner was given his debut in the second half, after he replaced the hopeless Micah Richards at half-time.
Then Eric Black possibly made the worst call of his reign as Villa manager so far, when he replaced the impressive Jordan Ayew with Rudy Gestede in the 59th minute as Villa looked for an equalizer.
However, it was Southampton who grabbed the fourth goal of the game, when Shane Long once again squared the ball for Tadic, who fired past Brad Guzan once again.
In the 74th minute, Villa fans continued their protests, with thousands walking out of the stadium, whilst those who remained held up posters saying ‘Proud History What Future?’.
Ashley Westwood gave the home fans something to cheer in the 85th minute, after he curled the ball past Forster from the edge of the penalty area after Southampton failed to clear a corner.
However, there was to be no comeback for Villa, as Saido Mane rose highest to direct a header past Brad Guzan to secure the win for the visitors with just seconds left on the clock.
Villa’s next game sees them travel to Vicarage Road, to face Watford next Saturday.
