Mix barbecue sauce and Worcestershire sauce until blended. Mix 1/3 cup barbecue sauce mixture with egg and onions in large bowl until blended. Add meat and bread crumbs; mix just until blended.
Shape meat mixture into 48 small meatballs; place on rimmed baking sheet sprayed with cooking spray.
Bake 6 min.; brush with 1/4 cup of the remaining barbecue sauce mixture. Turn meatballs; bake 5 min. or until done (160�F).
Meanwhile, mix remaining barbecue sauce mixture with sour cream in saucepan; cook on medium-low heat 3 to 5 min. or just until heated through, stirring frequently. (Do not let sauce come to boil.)
Serve meatballs with barbecue sauce mixture.