COMBINE all ingredients except steak.
PLACE steak in resealable plastic bag. Remove 1/4 cup of the steak sauce mixture; pour remaining steak sauce mixture over steak in bag. Seal bag, then turn bag over several times to evenly coat steak. Refrigerate at least 30 min. to marinate.
PREHEAT grill to medium heat. Remove steak from bag; discard marinade. Grill flank steak, uncovered, 17 to 21 min. (or skirt steak 10 to 13 min.) for medium-rare to medium doneness, turning occasionally and brushing with the reserved 1/4 cup steak sauce mixture.