In this study, we demonstrate a synergistic enhancement of photoluminescence (PL) in an atomically thin molybdenum disulfide (MoS₂) monolayer using a dual-laser-beam-assisted chemical modification method. A continuous-wave (CW) green laser, directed perpendicularly at the MoS₂, locally raises the temperature and induces the formation of sulfur (S) vacancies, resulting in a significant increase in PL intensity. Subsequently, a UV nanosecond laser beam laterally illuminates the area above the MoS₂ layer, breaking chlorine molecules and introducing chlorine radicals without damaging the sample. This process further enhances the PL in the region previously affected by S vacancies. The binding energy of chlorine atoms to S-vacancy sites is greater than that to the pristine MoS₂ surface, facilitating more effective p-type doping. The stronger interaction at the defect sites created by the CW laser contributes to the observed synergistic PL enhancement. Our approach presents a novel method for precise and spatially selective chemical doping in two-dimensional (2D) van der Waals (vdW) materials.