Reattachment to work (i.e., rebuilding a mental connection to work) before actually starting work is important for work engagement during the day. Building on motivated action theory, this study examines anticipated task focus, positive affect, and job resources (job control and social support) as mediators that translate reattachment in the morning into work engagement during the day. We collected daily-survey data from 151 employees (total of 620 days) and analyzed these data with a multilevel path model. We found that day-level reattachment to work in the morning predicted anticipated task focus, positive affect, social support, and job control through goal activation and that anticipated task focus, positive affect, social support, and job control predicted work engagement during the day. This study points to the important role of reattachment to work in employee experiences and behaviors throughout the workday and specifically highlights the benefits of such initial mental boundary crossing between life domains for employee engagement at work.