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Using numerical simulations, we study the atomic-scale frictional behaviors of monovacancy-defective graphene and single-layer molybdenum-disulfide (SLMoS₂) based on the classical Prandtl&#8722;Tomlinson (PT) model with a modified interaction potential considering the Schwoebel&#8722;Ehrlich barrier. Due to the presence of a monovacancy defect on the surface, the frictional forces were significantly enhanced. The effects of the PT model parameters on the frictional properties of monovacancy-defective graphene and SLMoS₂ were analyzed, and it showed that the spring constant of the pulling spring <i>c_x</i> is the most influential parameter on the stick&#8722;slip motion in the vicinity of the vacancy defect. Besides, monovacancy-defective SLMoS₂ is found to be more sensitive to the stick&#8722;slip motion at the vacancy defect site than monovacancy-defective graphene, which can be attributed to the complicated three-layer-sandwiched atomic structure of SLMoS₂. The result suggests that the soft tip with a small spring constant can be an ideal candidate for the observation of stick&#8722;slip behaviors of the monovacancy-defective surface. This study can fill the gap in atomic-scale friction experiments and molecular dynamics simulations of 2D materials with vacancy-related defects.