The presence of electronic phase separation in complex materials has been linked to many types of exotic behaviour, such as colossal magnetoresistance, the metal-insulator transition and high-temperature superconductivity; however, the mechanisms that drive the formation of coexisting electronic phases are still debated. Here we report transport measurements that show a preferential orientation of electronic phase domains driven by anisotropic long-range elastic coupling between a complex oxide film and substrate. We induce anisotropic electronic-domain formation along one axis of a pseudocubic perovskite single-crystal thin-film manganite by epitaxially locking it to an orthorhombic substrate. Simultaneous temperature-dependent resistivity measurements along the two perpendicular in-plane axes show substantial differences in the metal-insulator transition temperature and extraordinarily high anisotropic resistivities, which indicate that percolative conduction channels open more readily along one axis. These findings suggest that the origin of phase coexistence is much more strongly influenced by strain than by local chemical inhomogeneity.