The lack of an efficient support system for people with multiple, long-term health conditions has increased costs, worsened health outcomes, and prompted policymakers to implement a boundary-spanning role within healthcare settings. While scholars have demonstrated the benefits of coordination roles and other such high-performance work practices (HPWPs) in this sector, the actual implementation of these practices is less clear. Based on a comparative case study approach, 153 interviews, and other qualitative data, this article explores frontline managers' HR philosophies and practices (‘frontline HRM relationality’) to explain possible variation in efforts to implement the boundary-spanning role of care coordinators (CCs). Despite strong policy support for the role, coordination has improved unevenly because of varying degrees of HRM relationality: findings show that higher frontline HRM relationality was associated with lower inter-occupational professionalization differences and higher boundary-spanning coordination. The article contributes to a nascent literature on HPWP implementation by theorizing frontline HRM relationality as a continuum that moderates professionalization-related coordination problems and highlights the importance of frontline HRM relationality for implementing HPWPs in professionalized settings.