But two goals in three minutes at the death from Southern and veteran striker Brett Ormerod saw them complete a remarkable comeback.
It was the Seasiders' first home win since November 7 and Southern said: "It was a massive three points for us.
"Our home form had taken a dip over the last six or seven weeks so to pull that out of the fire and turn it around like that was unbelievable.
"That's a season defining moment as far as I'm concerned. Hopefully we can push on now and have a real charge again."