Combine liquid smoke, Worcestershire, garlic salt, onion and celery seed in small bowl. Place brisket in shallow non-metal dish, fatty side down. Pour marinade over meat; cover and refrigerate 8 hours or overnight.
Preheat oven to 300 degrees F (150 degrees C).
Remove meat from marinade and place in an ovenproof pan. Roast, fatty side up, 5 hours, until tender.