A new design of single-layered balanced filtering crossover with high selectivity based on square patch resonator is proposed. Originated from the degenerate modes, that is, TM and TM on square patch resonators, the feasibility of intrinsic common-mode (CM) suppression and channel isolation is conceived. For demonstration, a first-order balanced crossover prototype is designed. Afterwards, to enhance selectivity, a square patch resonator is subtly divided into two identical parts and then introduced into the prototype. Hence, a balanced filtering crossover with a fifth-order Chebyshev response is formed. Furthermore, stubs are deployed between adjacent patch resonators to introduce mixed couplings. Thus, two controllable transmission zeros are obtained, and better out-of-band suppression is achieved. Ultimately, the proposed crossover is fabricated and measured. High performance in terms of differential-mode filtering response, in-band CM suppression and channel isolation demonstrates the feasibility of the proposed method.