Brain tumours represent a burden for society, not only due to the risks they entail but also because of the possibility of losing relevant cognitive functions for the patient’s life after their resection. In the present study, we report how we monitored chess performance through a multimodal Electrical Stimulation Mapping (ESM) – functional Magnetic Resonance Imaging (fMRI) combined protocol. The ESM was performed under a left parietal lobe tumour resection surgery on a patient that expressed the desire to preserve his chess playing ability post-operative. We designed an ad-hoc protocol to evaluate processes involved in chess performance that could be potentially affected by the tumour location: (i) visual search, (ii) rule-retrieval, and (iii) anticipation of checkmate. The fMRI study reported functional regions for chess performance, some of them proximal to the lesion in the left parietal lobe. The most relevant result was a positive eloquent point encountered in the vicinity of the left supramarginal gyrus while performing the rule-retrieval task in the ESM. This functional region was convergent with the activations observed in the pre-operative fMRI study for this condition. The behavioural assessment comparison revealed post-operative an increase in reaction time in some tasks but correctness in performance was maintained. Finally, the patient maintained the ability to play chess after the surgery. Our results provide a plausible protocol for future interventions and suggest a role of the left supramarginal gyrus in chess cognitive operations for the case presented.