Spatial attention is the process through which we prioritize processing at specific locations in space, occurring through both the enhancement of behaviorally important locations and the suppression of potentially distracting locations. Despite extensive research demonstrating that goal-directed spatial attention can influence processing in various visual regions, debate persists regarding its timing, particularly its influence on initial afferent activity in early visual cortices. In this study, we aimed to address this question using human electroencephalography. We used the C1 component, which serves as a measure of initial afferent activity, based on its early onset (60 - 90 ms poststim) and consistent source localization. To evaluate goal-directed attentional modulation, we utilized alpha-band activity (8–14 Hz), a well-established neural marker of sensory suppression. Participants detected targets at a cued location while distractors (i.e., task-irrelevant stimuli) were presented at a non-cued location. We first replicated attentional modulation of the C1. We then replicated an increase in alpha band power over regions representing task-irrelevant sensory information—evidence of the alpha-related suppression. Finally, we investigated the relationship between C1 amplitude and pre-stimulus alpha power. The results revealed that higher alpha power was associated with lower C1 amplitudes at the distractor location and higher C1 amplitudes at the target location (i.e., at the attended location). This pattern of results was replicated in the majority of participants at the single-subject level. Overall, our findings provide the first evidence that initial afferent activity in early visual cortices can be actively suppressed through goal-directed, alpha-related gating of sensory processing.