  Using resonant X-ray spectroscopies combined with density functional
calculations, we find an asymmetric bi-axial strain-induced $d$-orbital
response in ultra-thin films of the correlated metal LaNiO$_3$ which are not
accessible in the bulk. The sign of the misfit strain governs the stability of
an octahedral "breathing" distortion, which, in turn, produces an emergent
charge-ordered ground state with an altered ligand-hole density and bond
covalency. Control of this new mechanism opens a pathway to rational orbital
engineering, providing a platform for artificially designed Mott materials.
