Lubricating oils play a vital role in industrial machinery, particularly in reducing the friction and wear at sliding interfaces. They typically contain a combination of various additives, and the chemical interactions between these additives can lead to synergistic effects or competitive reactions. However, the detailed mechanisms underlying these interactions remain unclear. This study investigates the effects of calcium sulfonate rust inhibitors with different total basic numbers on the wear resistance and tribofilm formation of lubricants containing zinc dialkyldithiophosphate (ZnDTP) and molybdenum dithiocarbamate (MoDTC). Macroscale friction tests using a reciprocating tribotester revealed that calcium sulfonate improved the wear resistance without compromising the low-friction properties of ZnDTP and MoDTC. Nanoscale evaluations conducted via in situ atomic force microscopy and scratch tests demonstrated that calcium sulfonate facilitated the formation of thicker and denser tribofilms, enhancing the wear resistance. Surface analysis using X-ray photoelectron spectroscopy and transmission electron microscopy revealed the presence of calcium compounds throughout the tribofilms formed with calcium sulfonate, which contributed to smoother and more uniform structures. These findings highlight the synergistic effects of calcium sulfonate with ZnDTP and MoDTC and offer insights into the optimization of additive combinations in lubricating oils to improve the performance and lifespan of industrial machinery.