Background: Accessibility to efficient and person-centered healthcare delivery drives healthcare transformation in many countries. In Singapore, specialist outpatient clinics (SOCs) are commonly congested due to increasing demands for chronic care. To improve this situation, the National University Health System (NUHS) Regional Health System (RHS) started an integrated care initiative, the Right-Site Care (RSC) program in 2014. Through collaborations between SOCs at the National University Hospital and primary and community care (PCC) clinics in the western region of the county, the program was designed to facilitate timely discharge and appropriate transition of patients, who no longer required specialist care, to the community. The aim of this study was to evaluate the implementation fidelity of the NUHS RHS RSC program using the modified Conceptual Framework for Implementation Fidelity (CFIF), at three distinct levels; providers, organizational, and system levels to explain outcomes of the program and to inform further development of (similar) programs. Methods: A convergent parallel mixed methods study using the realist evaluation approach was used. Data were collected between 2016-2018 through non-participatory observations, reviews of medical records and program database, together with semi-structured interviews with healthcare providers. Triangulation of data streams was applied guided by the modified CFIF. Results: Our findings showed four out of six program components were implemented with low level of fidelity, and 9,112 suitable patients were referred to the program while 3,032 (33.3%) declined to be enrolled. Moderating factors found to influence fidelity included: (i) complexity of program, (ii) evolving providers’ responsiveness, (iii) facilitation through synergistic partnership, training of PCC providers by specialists and supportive structures: care coordinators, guiding protocols, shared electronic medical record and shared pharmacy, (iv) lack of organization reinforcement, and (v) mismatch between program goals, healthcare financing and providers’ reimbursement. Conclusion: Functional integration alone is insufficient for a successful right-site care program implementation. Improvement in relationships between providers, organizations, and patients are also warranted for further development of the program.