We prove that a single-valued solution of perfectly competitive TU economies underlying nonatomic exact market games is uniquely determined as the Mertens  value by four plausible value-related axioms. Since the Mertens value is always a core element, this result provides an axiomatization of the Mertens value as a core-selection. Previous works in this direction assumed the economies to be either differentiable (e.g., Dubey and Neyman ) or of uniform finite-type (e.g., Haimanko ). Our work does not assume that, thus it contributes to the axiomatic study of payoffs in perfectly competitive economies (or values of their derived market games) in general. In fact, this is the first contribution in this direction.