Single-atom　catalysts　(SACs)　anchored　on　defective　supports　offer　exceptional　catalytic　efficiency　but　face　challenges　in　stabilizing　isolated　metal　atoms　and　optimizing　metal-support　interactions.　Here,　a　defect-driven　strategy　is　reported　to　construct　a　3D　dendritic　SAC　comprising　interwoven　ultrathin　TiO2　nanowires　(NWs)　with　abundant　oxygen　vacancies　(OVs)　that　stabilize　atomically　dispersed　cobalt　(Co)　sites.　Using　hydrothermal　synthesis　followed　by　acid　etching　and　calcination,　Ti　&　horbar;Co　&　horbar;Ti　motifs　are　engineered　at　OVs　site.　The　3D　architecture　provides　multiscale　porosity　and　charge　transport,　achieving　syngas　production　rates　of　28.4　mmol　g(-1)h(-1)　(CO)　and　13.9　mmol　g(-1)h(-1)　(H-2)　with　a　high　turnover　frequency　(TOF)　of　10.6　min(-1),　surpassing　many　other　state-of-the-art　Co-based　SACs.　In　situ　Raman　and　electron　paramagnetic　resonance　(EPR)　analysis　reveal　OVs　consumption　during　Co　anchoring,　while　density　functional　theory　(DFT)　validates　charge　redistribution　from　Ti　to　Co,　enabling　efficient　electron　transfer　and　inducing　strong　electronic　interactions　that　enhance　CO2　adsorption　and　activation.　The　results　highlight　the　interplay　between　atomic-scale　coordination　environments　and　macroscale　architectural　order　in　harnessing　the　catalytic　potential　of　SACs　and　ultrathin　1D　NWs.