Projects, as the common unit of organizing complex tasks, often feature unique challenges that require both radical innovation and incremental improvements to processes and solutions in order to deliver the project within constraints. Both exploration and exploitation are likely to be needed for complex engineering projects to succeed. This study, through an in-depth case study of a complex infrastructure project facing unique challenges and tight budget and schedule, investigates the antecedents of ambidexterity and the effect of ambidexterity on project performance. The main contributions of this research include finding: (1) ambidexterity at the project team level to be a significant contributor to project performance; (2) the effects of temporal separation and project context on project performance are mediated by the project team's degree of ambidexterity; and (3) contrary to the prediction from organizational literature, structural separation has not contributed to the case project team's ambidexterity. The authors believe that among the three antecedents for ambidexterity at the project level as predicted by organizational literature, structural separation is rendered ineffective by the natural cycling between exploration and exploitation in the project environment and by the need to integrate the two under time pressure and resource constraints. The development of an effective project context can facilitate the temporal cycling between exploration and exploitation by creating awareness that overcomes the inertia in transitioning between the two by setting performance expectations and appropriate social context. Implications for theory development and practice are discussed.