Atomically dispersed, non-noble-metal catalysts represent promising alternatives to costly platinum-group electrocatalysts, yet precise control over metal site proximity remains challenging. Herein, we report the synthesis of ultrathin (∼1.5 nm) N-doped carbon nanosheets decorated with densely packed single-atom copper sites (Cu SAs/N-CS), achieved via controlled pyrolysis of a Cu–1H-1,2,4-triazole complex precursor. The resulting Cu SAs/N-CS exhibits a high copper loading (3.17 wt %) with a remarkably short average interatomic distance (∼3.1 Å) between adjacent Cu atoms. Inspired by multicopper oxidase enzymes, these closely spaced Cu active sites facilitate efficient four-electron (4e–) oxygen reduction reactions (ORRs), displaying superior catalytic performance and long-term stability in both neutral and alkaline media. Specifically, Cu SAs/N-CS achieves impressive half-wave potentials of 0.68 V (neutral) and 0.91 V (alkaline) vs RHE, rivaling commercial Pt/C under neutral conditions and outperforming it in alkaline electrolytes. Density functional theory (DFT) analyses indicate that short-range Cu site proximity upshifts the d-band center, strengthens O2 adsorption, and significantly lowers the activation barrier for the 4e– ORR pathway, thus elucidating the mechanism behind its exceptional catalytic activity.