The study explores the influence of domestic competition on international trade performance, using data from a broad sample of Japanese industries. Domestic rivalry is measured directly using market-share instability rather than employing structural variables such as seller concentration. We find robust evidence that domestic rivalry has a positive and significant relationship with trade performance measured by world export share, particularly when R&D intensity reveals opportunities for dynamic improvement and innovation. Conversely, trade protection reduces export performance. These findings support the view that local competition—not monopoly, collusion, or a sheltered home market— pressures dynamic improvement that leads to international competitiveness.