The use of competition as a conflict-handling style aimed at win-lose end results has been highlighted by some researchers to be common during project execution. However, the impact of such competition on project performance remains largely under-researched. This article seeks to address this gap in the existing literature. A system dynamics simulation model of competition between two key project participants (client and engineering consultant) was formulated through a mixed methods research methodology incorporating the system dynamics approach. Data gathered for two sets of unique projects were used separately to conduct model calibrations, simulation experiments, and impact analyses. The results suggested that the competition negatively influenced project performance.