Purpose This study aims to investigate the effects of project-level external knowledge search breadth and search depth on the innovation performance of open innovation (OI) projects in large firms; it further considers these effects mediated by two forms of control mechanisms (process and outcome control) when the level of project complexity and the two stages of a project – early (problem definition) and late (solution development) – are taken into account. Design/methodology/approach Based on a survey of 187 managers responsible for an OI project, the authors use theory on behavioral-based control mechanisms to explore whether the effect of external knowledge search breadth and depth on OI performance is contingent on having the right levels of control mechanisms in place. Findings The results showed that the control mechanism mediates the relationship between external knowledge search breadth and depth and OI project performance. Furthermore, project complexity is an important moderator of these effects, especially for outcome control. Originality/value A better OI project’s performance is not achieved by external knowledge search breadth and depth alone, but by building process and outcome control mechanism on it to balance knowledge sharing and protecting tension. Furthermore, Outcome control is only helpful with less complex OI projects.