In this article, we have judiciously interfaced copper oxides with graphitic carbon nitride (g-C3N4) from thermal reaction of melamine and copper sulfate in a one-pot protocol and manipulated the perforated sheet morphology thereafter. The CCN-X (X = 30, 40, 50, 60, and 70, depending on the wt % of CuSO4·5H2O) nanocomposites were prepared by homogenously mixing different percentages of CuSO4·5H2O with melamine from a solid-state thermal reaction in a furnace in air. Drastic lowering of CuSO4 decomposition temperature due to Cu(II)-amine complex formation and subsequent reduction of Cu(II) species by in situ produced ammonia (NH3) resulted in the production of CuO and catalytic amount of Cu2O, homogeneously dispersed within the perforated g-C3N4 nanosheet. How perforated sheet morphology evolved by combined effect of NH3, released from thermal condensation of melamine ensuring two-dimensional (2D) growth, and sulfur trioxide (SO3), expelled from CuSO4·5H2O facilitating the perforation, yielding better catalytic performance, has been elucidated. Excess NH3 from added NH4Cl removed perforation and ensued a marked decrease in efficacy. However, a high proportion of CuSO4·5H2O ruptured the framework of 2D sheets because of excess SO3 evolution. Among the different nanocomposites synthesized, CCN-40 (CuO-Cu2O/g-C3N4) showed the highest catalytic activity for 4-nitrophenol reduction. Thus, enhanced efficiency of the copper oxide catalyst by interfacing it with an otherwise inactive g-C3N4 platform was achieved.