In a small bowl whisk together celery salt, garlic powder and onion salt. Season both sides of the brisket. Place meat in a foil lined baking pan that is enough to fully enclose the meat. Pour Worcestershire sauce over the meat and as it drips to the side lift meat up so the liquid also seasons under the meat.
Crimp the foil tightly over the meat. Return to the refrigerator an hour.
Bring the meat to room temperature (30 minutes) and bake at 275 degrees for 5 hours. Remove foil and pour about 1 cup of barbecue sauce over the meat. Close the foil around the brisket and place back in the oven for another 30 minutes with the oven OFF.
Cool and slice into thin pieces.