Preheat the oven to 325 degrees F. Rinse the corned beef and pat dry. Sprinkle with salt, pepper and paprika. Place the meat with the fat side up in a shallow roasting pan. Spread the chili sauce over the top. Place the onion, celery and garlic around the meat. Pour 1 cup of water into the pan around the meat. Bake, uncovered, for 1 hour.
Carefully pour the beer over the brisket without rinsing off the chili sauce. Cover with aluminum foil and cook until very tender, about 3 hours more.
Remove the meat to a cutting board and let rest for 10 minutes. Slice thinly against the grain.
Skim any fat off the surface of the sauce with a metal spoon. Platter the meat and pour the sauce over it. Sprinkle with the parsley.