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When wind-excited tall buildings undergo vibrations beyond their linear elastic range, it becomes imperative to account for both strength and stiffness degradation and P-Delta effects. This study investigates the influence of the degradation and P-Delta effects on the inelastic response of wind-excited tall buildings through a reduced-order building model, wherein the alongwind and crosswind building responses are presumed to be contributed by the fundamental modes. The backbone curves of the hysteretic relationships between the generalized restoring forces and displacements are developed through monotonic static modal pushover analysis utilizing a high-fidelity finite element building model with consideration of P-Delta effect. A cyclic modal pushover analysis is performed to ascertain the degradation of generalized building stiffness and strength in both translation directions, stemming from the deterioration of steel material in stiffness and strength. Subsequently, a biaxial hysteretic force model is employed to depict the hysteretic relationships between generalized forces and displacements, factoring in degradation and P-Delta effects. The inelastic response of a 60-story steel building subjected to both alongwind and crosswind load excitations is quantified through response history analysis to assess the accuracy of the reduced-order building model and to evaluate the influence of degradation of material strength and pre-yield stiffness and P-Delta effects on various responses.