Long proved the pivotal figure in the 4-2 win and his goal that put the Saints ahead at Villa Park means he has scored more times -- six -- against the hapless Midlanders than any other Premier League opponent.
He also had another disallowed and set up both goals for Dusan Tadic in a man-of-the-match display that kept Southampton's hopes of European football next season simmering.
The Saints remain in eighth place, just a point behind Liverpool and two behind sixth-placed West Ham but they have played a game more than their rivals.
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Irishman Long, who has had a stop-start career in his two years at the club, was linked with a move to Liverpool in last January's transfer window but has now become a regular in Southampton's starting line-up.
Six goals in his last seven appearances suggest he is coming into form at just the right time with the European Championships approaching.
Long is a key member of Martin O'Neill's Republic of Ireland squad and will go into the tournament in France on the back of his best-ever Premier League season with nine goals.
On Saturday Long's starring role was bad news for his marker Joleon Lescott, who was blamed by the crowd for poor marking as the Irishman started to look a world beater.
Lescott, who had last week described Villa's relegation as "maybe a weight off the shoulders", found himself on the receiving end of much abuse on another fractious afternoon at Villa Park.
Southampton manager Ronald Koeman admitted the crowd's hostility to their own players gave the afternoon an odd feel.
"It was difficult because it was a strange atmosphere -- but even more so for the home team. It's a shame that Aston Villa have been relegated because it is a great club and stadium. I hope they are back before too long."
Villa's caretaker manager Eric Black did not criticise the supporters for their barracking.
"The fans are entitled to vent their displeasure. It's not an ideal atmosphere but it's understandable, given the circumstances," said Black. "We have to continue to be professional."
(Reporting by Neil Robinson, editing by Ian Chadband)
