Bulgaria's chances of reaching next year's finals vanished on Saturday when they lost 4-1 to Cyprus but Georgia scarcely had a shot on goal as the hosts tore into them from the start.
Manchester United's Berbatov completed his hat-trick within 29 minutes to take his Bulgaria tally to 46, just one goal short of Hristo Bonev's national record.
Bulgaria's triumph, seen by one of the smallest-ever crowds at the Vasil Levski national stadium, was helped by errors from Georgia keeper Giorgi Lomaia.
"You don't score six goals in a World Cup qualifier every day," said Bulgaria coach Stanimir Stoilov.
"The fans should believe in the national team and I hope we'll play in front of a capacity crowd next time."
Berbatov said: "There's nothing unusual in Bulgaria's failure to reach the finals as we don't have quality players for every position.
"The fans should be realistic and accept the reality. There's a lot of work to be done."
