Patients with mild cognitive impairment (MCI) show reduced top-down control, the ability to ignore task-irrelevant information. It is unclear whether this reduction corresponds with decreased brain connectivity. We aimed to determine whether and how differences in functional connectivity, or the correlated activity between brain areas, explain differences in top-down control in MCI. Twenty-six patients with MCI (mean age: 71.2 ± 8.9 years; 10 females) and 29 age-matched healthy older adults (mean age: 68.2 ± 4.6 years; 9 females) underwent neuropsychological assessment to confirm diagnosis and cognitive status. We used resting-state functional magnetic resonance imaging at 3T to analyze functional connectivity. Top-down control was estimated with a theory of visual attention (TVA)-based verbal partial-report task (parameter α; higher α indicates poorer control). We identified visual and attention-relevant functional brain networks and tested for differences between patients and controls while controlling for age and sex. Patients with MCI showed lower functional connectivity in the left frontoparietal (FPN) and visual network (VN). Patients also had worse top-down control than healthy controls (p = 0.031). The FPN, but not the VN, significantly correlated with top-down control across participants (r = -0.39, p = 0.003) and in the patient group (ρ = -0.48, p = 0.014). Moreover, FPN connectivity mediated the relationship between MCI and top-down control. These results indicate that lower FPN connectivity explains worse attentional control in MCI. Top-down control might explain memory decline in patients with MCI; longitudinal data are needed to establish prognostic value.