The relative contributions of individual components of multimodal diabetes management to glycemic control remain unclear in real-world primary care settings. This observational pre–post study enrolled 100 adults with type 2 diabetes in a 12-week, nurse-led four-pillar program integrating patient education, physical activity guidance, dietary counseling, and medication adherence monitoring. Multiple linear regression examined the simultaneous associations between behavioral predictors and changes in HbA1c (ΔHbA1c). Mean HbA1c reduction was 2.72 ± 1.25% (95% CI: 2.48–2.96), exceeding the clinically meaningful threshold (>0.5%). The regression model was statistically significant (F(4,95) = 5.16; p = 0.0008; R² = 0.178). Medication adherence independently predicted ΔHbA1c (unstandardized B = 0.327; standardized β = 0.216; p = 0.023), whereas diabetes knowledge, physical activity, and dietary adherence were non-significant (p > 0.05). A structured, nurse-coordinated four-pillar program achieved substantial short-term glycemic improvement among adults with type 2 diabetes, with medication adherence emerging as the strongest behavioral predictor. While comprehensive, multidimensional care remains essential for sustainable self-management, systematic adherence monitoring may optimize metabolic outcomes in routine clinical practice. Causal inference is limited by the observational pre–post design and potential residual confounding; future randomized controlled trials with extended follow-up and objective adherence measures are warranted to clarify component-specific effects and long-term sustainability