The present study addresses the quality problems commonly found in Peruvian SMEs in the plastic sector. These enterprises typically exhibit high levels of process variability, low efficiency, and an average sector defect rate of 6.6%. These challenges are intensified in make-to-order (MTO) environments, where frequent product changes and manual tasks increase operational instability. However, existing studies have not proposed methods specifically aimed at reducing defect rates in MTO SMEs, leaving a gap in approaches that directly target defect generation under high-variability conditions. In order to address this gap, the present research proposes an integrated defect-reduction model based on the application of Standard Work, Poka Yoke and Business Process Management (BPM). The model was implemented and validated through a pilot deployment in a Peruvian MTO plastics SME characterized by limited automation, high manual dependence, and underdeveloped process structures, providing a setting distinct from the more stable and technologically mature firms examined in prior studies. The results indicate a reduction in the total defect rate from 14.91% to 7.84%, accompanied by enhanced stability in critical manual operations. The findings demonstrate that combining Standard Work, Business Process Management, and Poka-Yoke can directly address defect sources in MTO plastics SMEs, offering a practical, low-cost, and replicable approach for improving quality in similar emerging-economy contexts.