Designing stable single-atom electrocatalysts with lower energy barriers is urgent for the acidic oxygen evolution reaction. In particular, the atomic catalysts are highly dependent on the kinetically sluggish acid–base mechanism, limiting the reaction paths of intermediates. Herein, we successfully manipulate the steric localization of Ru single atoms at the Co3O4 surface to improve acidic oxygen evolution by precise control of the anchor sites. The delicate structure design can switch the reaction mechanism from the lattice oxygen mechanism (LOM) to the optimized adsorbate evolution mechanism (AEM). In particular, Ru atoms embedded into cation vacancies reveal an optimized mechanism that activates the proton donor–acceptor function (PDAM), demonstrating a new single-atom catalytic pathway to circumvent the classic scaling relationship. Steric interactions with intermediates at the anchored Ru–O–Co interface played a primary role in optimizing the intermediates’ conformation and reducing the energy barrier. As a comparison, Ru atoms confined to the surface sites exhibit a lattice oxygen mechanism for the oxygen evolution process. As a result, the delicate atom control of the spatial position presents a 100-fold increase in mass activity from 36.96 A gRu(ads) –1 to 4012.11 A gRu(anc) –1 at 1.50 V. These findings offer new insights into the precise control of single-atom catalytic behavior.