This paper proposes a method of opening a zippered plastic bag by a dual-armed robot. The proposed method introduces sticky claw-like fingertips that support two actions: widening the closed bag rim and unzipping the zipper. Rim grasping is achieved by adhering the fingertips to the rim and spreading the arms to enlarge the gap, enabling reliable finger insertion. Zipper unzipping is performed by rotating the claw-like fingertips, generating a large unzipping force through the principle of a lever without requiring strong gripping forces. Experiments using three different zippered plastic bags were conducted to verify the effectiveness of the fingertips and motion.