1. Lightly grease a 6-qt. slow cooker; add onion and garlic. Stir together chili powder and next 5 ingredients. Rub over brisket; place brisket over onion mixture in slow cooker.
2. Whisk together beer and chili sauce. Slowly pour mixture around brisket (to avoid removing spices from brisket).
3. Cover and cook on LOW 7 to 8 hours (or on HIGH 4 to 5 hours) or until fork-tender. Uncover and let stand in slow cooker 20 minutes.
4. Remove brisket from slow cooker; cut brisket across the grain into thin slices. Return brisket to slow cooker, and spoon pan juices over meat.
We tested with Heinz Chili Sauce.