Competitive H₂ oxidation severely limits CO₂ selectivity (typically <50%) during preferential CO oxidation (CO-PROX) on Pt catalysts. While metal–oxide interfaces can potentially circumvent this trade-off, constructing architectures that spatially decouple CO and H₂ activation remains challenging. Here, we report a junction-confined FeO-Pt/SiO₂ catalyst in which FeO species selectively decorate Pt nanoparticles, creating well-defined and closely contacted interfacial sites. Unlike randomly distributed FeO in conventional catalysts, this configuration enables electron redistribution from Pt to FeO, as revealed by Bader charge analysis. This electronic effect preserves strong CO adsorption on Pt (required for CO activation) while dramatically enhancing O₂ activation at the interface. Consequently, CO oxidation proceeds via a dominant low-barrier interfacial pathway (0.20 eV), while weakened H₂ adsorption at the FeO–Pt junction mitigates competitive H₂ oxidation under H₂-rich conditions. The catalyst achieves >70% CO₂ selectivity at complete CO conversion over 80–160 °C and maintains stability for 100 h without noticeable deactivation under H₂-rich conditions. This work demonstrates that precise spatial organization of metal–oxide interfaces can effectively decouple competitive reaction pathways, offering a generalizable strategy for designing selective oxidation catalysts beyond CO-PROX.