Conflicting results in Y-Balance Test (YBT) performance are found when participants are exposed to acute physical fatigue (APF). Even though APF is known to impair isolated neurocognitive performance, the effects of APF on reactive balance test (RBT) performance have never been investigated. Furthermore, research on the underlying APF-induced neurophysiological mechanisms during these functional tests is scarce to non-existent. Therefore, the aim was to assess the influence of APF on two clinician-friendly balance tests: the YBT and RBT, as well as its effects on brain activity. Twenty healthy adults participated in this randomized crossover study. APF was induced by a 30 seconds modified Wingate test. YBT performance was expressed in maximal reach distances, and RBT performance involved visuomotor reaction time and accuracy. Electroencephalography (EEG) was used to measure brain activity during these balance tests. Balance test performance and EEG recordings were analyzed pre-post. APF was successfully induced given that secondary outcome measures (eg, heart rate, blood lactate concentration) significantly increased following the modified Wingate. Decreased RBT accuracy was observed after APF, yet YBT performance and RBT visuomotor reaction time were unaffected. APF induced spectral power increments in the brain during both YBT and RBT performance.