Rub tenderloin with salt, pepper, and garlic powder. Place tenderloin on a rack in a shallow roasting pan. Tuck narrow end under to make roast more uniformly thick. Insert meat thermometer, if desired.
Bake, uncovered, at 450° for 45 minutes or until meat thermometer registers 140° (rare). Cover; set aside and keep warm.
Combine wine, water, mushrooms, and parsley in a medium saucepan. Bring to a boil; reduce heat, and simmer 10 minutes or until mushrooms are tender.
Cut tenderloin into 1-inchthick slices, and arrange on a heated platter. Serve with mushroom sauce.