This paper presents a discrete-time approach to the design of proportional–integral (PI) controllers for second-order systems, focusing on stability region mapping and performance enhancement via delay augmentation. Unlike conventional tuning in the continuous domain, direct discrete-time analysis enables a more accurate characterization of the sampled dynamics. The methodology derives the complete set of stabilizing \((k_p, k_i)\) gains and identifies the fastest stabilizing controller by maximizing the closed-loop decay rate. The framework is then extended to a proportional–integral–retarded (PIR) structure by introducing intentional delays in the feedback path. The stability boundaries are mapped in the augmented gain space and the performance is compared with classical PI control. Simulation results show that appropriately tuned delays can expand the achievable performance limits, achieving faster settling times while preserving zero steady-state error and robustness.