Preheat oven to 350 degrees. Combine ground chuck, onion, egg, bread crumbs, soup mix, tomato sauce, Worcestershire sauce, and pepper in a large mixing bowl and shape into a loaf. Place into loaf pan.
Combine ketchup with reserved 3 tablespoons Worcestershire sauce; brush on top of meatloaf.
Place in oven and bake 45 to 50 minutes. Remove and let stand 10 minutes before slicing.