Objective: This study focused on the effect of γ-aminobutyric acid (GABA) intake on psychological state and game performance during esports gameplay. Methods: A randomized, double-blind, placebo-controlled crossover study was conducted with eight healthy male university students aged 20–24 years who regularly play esports. The participants ingested either 200 mg of GABA or a placebo prior to gameplay and then completed a standardized esports task using the Mobalytics Proving Ground™ (MPG), a perceptual-cognitive task within “League of Legends” designed to train and evaluate player performance. Subjective psychological states were assessed pre- and post-gameplay using the Profile of Mood States 2 (POMS2^®) short version. Esports task performance was evaluated based on MPG scores. Results: GABA intake significantly reduced psychological confusion–bewilderment and fatigue in the POMS 2^® short version during esports gameplay. Furthermore, the game scores were significantly higher in the GABA group compared to the placebo group. Conclusions: These findings suggest that GABA intake may serve as a potential strategy to enhance both the mental state and performance of esports players.