Due to the advent of the pandemic, online learning was fully introduced into the Philippine educational setup. One of the emerging challenges that online teachers face is fostering student engagement in virtual classrooms. Thus, this paper aimed to examine the predictors of student engagement in online learning. The mediating role of self-regulation in the relationship between instructor scaffolding for interaction and student engagement in online learning was explored. The data from a total of 1217 undergraduate students who were enrolled during the research in a public or private university in Pampanga were analyzed. The correlation among variables was also examined. Mediation analysis using Process Macro was performed. The results revealed that instructor scaffolding for interaction and self-regulation predicted student engagement in online learning. Self-regulation served as a partial mediator. With these findings, developmental programs to promote scaffolding for interaction strategies and self-regulatory behaviors in online learning were proposed to foster student engagement.