Light-driven energy conversion devices call for the atomic-level manipulation of defects associated with electronic states in solids. However, previous approaches to produce oxygen vacancy (V<sub>O</sub>) as a source of sub-bandgap energy levels have hampered the precise control of the distribution and concentration of V<sub>O</sub>. Here, a new strategy to spatially confine V<sub>O</sub> at the homo-interfaces is demonstrated by exploiting the sequential growth of anatase TiO<sub>2</sub> under dissimilar thermodynamic conditions. Remarkably, metallic behavior with high carrier density and electron mobility is observed after sequential growth of the TiO<sub>2</sub> films under low pressure and temperature (L-TiO<sub>2</sub>) on top of high-quality anatase TiO<sub>2</sub> epitaxial films (H-TiO<sub>2</sub>), despite the insulating properties of L-TiO<sub>2</sub> and H-TiO<sub>2</sub> single layers. Multiple characterizations elucidate that the V<sub>O</sub> layer is geometrically confined within 4 unit cells at the interface, along with low-temperature crystallization of upper L-TiO<sub>2</sub> films; this 2D V<sub>O</sub> layer is responsible for the formation of in-gap states, promoting photocarrier lifetime (≈300%) and light absorption. These results suggest a synthetic strategy to locally confine functional defects and emphasize how sub-bandgap energy levels in the confined imperfections influence the kinetics of light-driven catalytic reactions.