This research explores the creation of high-performance cementitious mortars incorporating graphene oxide (GO) and micro-silica, with a particular emphasis on their use in repair applications. The effectiveness of these mortars is assessed in comparison to those based on nano-silica. Mortar mixtures were formulated with a fixed 8% micro-silica content and varying GO concentrations (0.025%, 0.05%, 0.075%, and 0.1% by cement weight), while nano-silica mixtures included 1% nano-silica and a reduced amount of micro-silica. Extensive mechanical testing, including compressive, split tensile, and flexural strength assessments, was performed after 7, 14, and 28 days of curing. The mixture with 8% micro-silica and 0.05% GO demonstrated superior mechanical properties in all tests. However, increasing GO concentrations resulted in diminished strength due to inadequate dispersion and agglomeration. Microstructural evaluations (SEM, EDS) indicated enhanced matrix densification and interfacial transition zones (ITZ) at optimal GO levels. Among all the mixtures tested, the combination of 8% micro-silica and 0.05% GO (with 957.6 kg/m3 OPC, 1064 kg/m3 crushed sand, and 0.5% superplasticizer) achieved the best overall performance, highlighting the potential of nano-engineered materials in advanced repair mortars.