A binary liquid mixture, containing the Lennard-Jones molecules A and B, in equilibrium with a bulk liquid reservoir near the point of phase separation, confined between atomistic chemically patterned walls, is studied by grand canonical Monte Carlo simulations. In the bulk, the B-rich phase is stable and the A-rich phase is metastable. The walls bear patches attractive to A; when the walls are close, A-rich liquid bridges condense between the patches. The normal and lateral forces on the walls are measured as a function of the wall separation and of the lateral displacement between the patches on opposite walls. When there are one or two molecular layers in the bridge and the wall lattice constant is close to that of crystalline A, the normal and lateral forces depend strongly on the registry of the wall lattices, varying in an oscillatory manner.