<p>Anticipated reductions in agricultural water resources, driven by increasing demands and the enduring impacts of climate change, necessitate a critical reevaluation of irrigation practices. This study investigates the efficacy of innovative water-saving techniques, specifically partial-root zone drying (PRD)—a deficit irrigation method that alternates wetting and drying opposite sections of a plant’s root system—and conventional deficit irrigation (DI). The experiments were conducted in a controlled glasshouse environment using the potato cultivar Mondial. Over two growing seasons, four distinct irrigation levels, corresponding to 50%, 70%, 80%, and 100% of field capacity were implemented and evaluated for PRD and DI treatments. The research focuses on assessing how PRD and DI affect various physiological parameters of potatoes. Both irrigation strategies significantly reduced leaf water potential (LWP, Ψ_L) and stomatal conductance (<i>gs</i>), with PRD showing more pronounced decreases under PRD-50% and DI-50%. Moreover, chlorophyll content increased under water stress, with no significant differences observed between PRD and DI treatments at the same irrigation levels. The amount of irrigation predominantly influenced relative water content (RWC). Although there was variability in the Maximum Quantum Efficiency of Photosystem II (Fv/Fm) across treatments, statistical analysis revealed no significant differences between irrigation levels or methods, suggesting a similar impact on PS II during the vegetative-tuberization phase. These findings indicate that while PRD and DI can effectively conserve water, PRD demonstrates significant advantages by enhancing water stress responses under mild water restriction, particularly by improving water-related traits and potentially maintaining productivity. However, at 50% of field capacity, PRD induces more pronounced stress responses, making it less suitable than DI for sustaining plant functionality under such conditions.</p>