Our study explores the influence of congruence between a brand’s positioning and the game rules in advergames, highlighting the importance of procedural congruence in the advertising effectiveness of an advergame. Using a 2*2 between-subjects experiment, congruence is manipulated through the cooperative status of a company and cooperative and competitive game rules. The results reveal that high congruence enhances the perceived legitimacy of the advergame, leading to positive attitudes towards both the advergame and the brand, as well as a higher purchase intent. Our findings highlight the importance of aligning game rules with brand positioning in advergame design and contribute to understanding the role of legitimacy in the persuasive process of advergames. Academic and managerial implications are discussed.