Add celery, onion, garlic, & liquid smoke to trimmed beef brisket. Cover tightly and refridge overnight.
Take marinated beef and add salt, pepper & worschestshire sauce. Cover brisket tightly with foil and bake at 275 degrees for 5 hours.
Remove brisket from oven, uncover and add 6 oz. BBQ sauce. Return uncovered brisket to oven and bake for 1 hour at 275 degrees. Let beef stand for 1/2 hour before slicing.