The England defender smashed in a late leveler just as Villa looked set to clinch its first win in eight games.
Gabby Agbonlahor had opened the scoring after rounding
the outrushing Fraser Forster in the 29th as Southampton looked far from
its best.
The visitors dominated possession but failed to regularly
test goalkeeper Brad Guzan, while Villa was left to rue Andi Weimann's
glaring miss on a counterattack in the 78th.
The point did at least lift Villa up to 16th while Southampton slipped six points behind leader Chelsea, but still two points ahead of Manchester City.