Distributed energy resources have become a key element towards a smarter grid. However, several significant challenges for real-time implementation have emerged, in particular control design and its integration with distribution systems. In this work, a fully distributed dynamic transactive control to coordinate distributed energy resources in a distribution system considering physical network constraints based on saddle-point dynamics with a predictive-sensitivity conditioning term is proposed. An alternative interconnection of dynamical systems in different timescale preserving stability and optimality is introduced. A stability result for saddle-point dynamics with predictive-sensitivity conditioning is presented. Finally, simulation results for a distribution network with distributed energy resources adopted from an IEEE 37-bus test feeder are implemented to validate numerically the proposed approach.