This paper analyzes the incentives of large shareholders to implement the corporate governance system that favors their interests within a framework of highly concentrated ownership and poor legal protection for investors. A metric for corporate governance based on the fulfillment of non-mandatory rules of good corporate governance is used. System GMM (Generalized Method of Moments) estimates for a balanced panel data of Brazilian firms reveal that the ownership concentration is detrimental to corporate governance quality and the quality of board composition. In accordance with the expropriation effect on principal-principal agency conflicts, by weakening the corporate governance system and board composition, large controlling shareholders may use private benefits of control. As proposed by the substitution effect, in a complementary way, controlling shareholders may renounce strong boards and directly perform management monitoring, mitigating agency conflicts with managers. Finally, the ability of large shareholders other than the main blockholder is not enough to contest his/her power to shape the corporate governance system. The work provides evidence of the prominence of the principal–principal agency problem in an emerging market, by analyzing the effect of ownership concentration over the quality of the corporate governance system, and also that other large non-controlling shareholders are not able to contest the power of the main blockholder.