David Norris’ equaliser deep into stoppage time denied Saints victory in the south coast derby.
Saints twice led through Billy Sharp goals but were pegged back on both occasions at St Mary’s.
Sharp’s first came after 28 minutes only for Chris Maguire’s fierce drive to level things up eight minutes later.
Saints were not at their best but thought they won it when Sharp flicked home from close range with just a minute of the game remaining, the goal initially ruled out for offside before referee Neil Swarbrick reversed the decision.
But Norris’ remarkable strike in the dying seconds of the game meant Saints had to settle for a point.
It took them back to the top of the table on goal difference, now level with second placed Reading and four ahead of third placed West Ham with five games left.