Optimization of Pt atom utilization efficiency is critical for the development of proton-exchange-membrane fuel cells. Here we aim to develop an efficient oxygen reduction reaction (ORR) catalyst with a low Pt content through the concurrent modification of Pt-Co alloy catalysts and carbon substrate. In the present study, ultrafine Pt-Co alloy nanoparticles are successfully synthesized and stabilized by topological carbon defects via adopting the ammonia thermal treatment. Despite the low Pt loading, the obtained catalyst exhibits an impressive half-wave potential of 0.926 V versus the reversible hydrogen electrode in 0.1 M HClO₄ electrolyte. Furthermore, the durability testing using the timed-current method demonstrates a tiny loss of only 3.6% after 12 h. Both experimental results and theoretical calculations demonstrate that topological carbon defects significantly enhance the charge transfer processes at the alloy/carbon interface, contributing to the strong electronic metal-support interactions between the Pt-Co alloy nanoparticles and topological carbon defects. These interactions, along with the alloy effect, play a crucial role in promoting the ORR performance in acidic media.