Study on magnetism in two-dimensional (2D) spin−lattices is advancing rapidly. In this work, phase-pure botallackite (Bo) (Cu₂(OH)₃Br), a quasi-2D S = 1/2 anisotropic triangular spin−lattice is stabilized over 2D reduced graphene oxide (rGO) nanosheets via simple oxidation−reduction reaction chemistry. In comparison to polycrystalline Bo, such an anchoring resulted in the oriented growth of Bo crystallites in the Bo-rGO system. The Bo-rGO nanocomposite was found to be magnetically active with a Néel transition at ∼8.9 K, crossing over to possible XY anisotropy at ∼5 K−as revealed by complementary dc and ac susceptibility measurements−an unprecedented observation in the field assigned to an interfacial effect. This work demonstrates the potential usage of nonmagnetic 2D functionalized graphene to significantly modulate the magnetic properties of 2D spin−lattices.