The paper deals with the tracking output variable of nonlinear SISO-system for a given signal with some accuracy under unmatched external disturbances and functional uncertainties within the restrictions on state variables and control. A new approach, based on expansion of the state space via filters with discontinuous inputs is designed. Organization of sliding modes on manifolds of the virtual states space of the extended system allows us to reduce the stabilization problem of the tracking error to the stabilization problem of filters variables with given accuracy and ensure boundedness and continuity of variables in a closed-loop system. This approach extends the class of admissible systems by nonlinear systems with non-smooth disturbances, where special requirements for the arguments composition of functional uncertainties not needed.