Trim fat from brisket. If necessary, cut to fit into crock pot.
Combine chili powder, garlic powder, celery seed and pepper; rub evenly over meat. Place meat in a 3 1/2-5 quart crock pot.
For sauce, combine catsup, chili sauce, brown sugar, vinegar, Worcestershire sauce, liquid smoke and dry mustard. Pour over brisket.
Cover; cook on low setting for 8 to 10 hours or on high for 4 to 5 hours. Remove meat from cooker. Cut the brisket into thin slices across the grain. Skim fat off juices in cooker; serve juices with meat.