Combine the brown sugar, chile powder, cumin, celery salt, garlic, and salt and pepper to taste in a small bowl. Rub all over the brisket, then transfer to a 5-to-6-quart slow cooker. Combine 3/4 cup ketchup, the vinegar and Worcestershire sauce in another small bowl. Pour over the brisket along with 3/4 cup water. Cover and cook on low, 8 hours.
Remove the brisket to a cutting board and let rest 10 minutes. Meanwhile, skim off the excess fat from the sauce; stir in the remaining 1/2 cup ketchup. Reserve one-third of the brisket (about 12 ounces) and 1 cup of the brisket sauce for Southwestern Brisket Hash. Slice the remaining brisket and divide among plates. Top with some of the sauce and serve with potato salad and cornbread.
Per serving: Calories 453; Fat 12 g (Saturated 5 g); Cholesterol 115 mg; Sodium 676 mg; Carbohydrate 16 g; Fiber 0 g; Protein 67 g