Potato is one of the most important food crops for human consumption. The obligate biotrophic pathogen Spongospora subterranea infects potato roots and tubers, resulting in considerable loss of potato tuber yield and quality. A comprehensive understanding of how potato plants respond to S. subterranea infection is essential for the development of pathogen-resistant crops. Here we employed label-free proteomics and phosphoproteomics to quantify protein-level responses of the susceptible and resistant potato cultivars in response to S. subterranea. A total of 2669 proteins and 1498 phosphoproteins were quantified in the leaf samples of the different treatment groups. Following statistical analysis of the proteomic data, oxidoreductase activity, electron transfer, and photosynthesis were identified as significant processes that differentially changed upon infection specifically in the resistant cultivar and not in the susceptible cultivar. The phosphoproteomics results indicated increased activity of signal transduction and defence response functions in the resistant cultivar. In contrast, the majority of increased phosphoproteins in the susceptible cultivar were related to transporter activity and localisation. This study provides new insight into the molecular mechanisms involved in potato resistance to S. subterranea infection and has highlighted the critical roles of protein phosphorylation in the regulation of potato immune response.