Construction projects continue to experience persistent schedule delays that adversely affect cost efficiency, quality, productivity, and stakeholder satisfaction. Although prior studies have extensively examined the causes of delays, limited empirical evidence explains how integrated managerial success conditions proactively improve delay mitigation capability. This study investigates the structural relationships among Key Success Factors (KSF), Project Readiness (PR), and Delay Mitigation (DM) in construction projects. The analysis primarily focuses on delay mitigation during the construction execution phase, where managerial capability and project readiness directly influence schedule performance and disruption response. A quantitative research design was employed using questionnaire data collected from 308 construction professionals in Thailand. KSF was conceptualized as a higher-order construct reflected by Project Execution Capability, Managerial and Digital Support, and Supply Chain Capability. Data was analyzed using Exploratory Factor Analysis, Confirmatory Factor Analysis, and Structural Equation Modeling. The findings indicate that KSF significantly enhances both Project Readiness and Delay Mitigation, while Project Readiness positively contributes to delay mitigation performance and partially mediates the relationship between managerial capability and project delay mitigation outcomes. The study provides an integrated capability-based framework and practical guidance for improving project delivery performance in uncertain construction environments.