For nonlinear single-channel systems with unmatched disturbances that can be represented in a triangular "input - output" form, a decomposition procedure for the synthesis of dynamic feedback is developed within the framework of the block approach. The procedure involves the synthesis of discontinuous control, providing tracking of the output variable of the command signal under the assumption of the smoothness of external influences; synthesis of a lower-order high-gain observer, which, based on measurements of the tracking error, estimates a mixed variable by which feedback is formed.