According to the conventional view competition law differs from regulation in that it is applied ex post, through proscriptions, and in a ‘crime-tort’ fashion. From this angle, when competition enforcers intervene ex ante, in a prophylactic manner, and employ prescriptive tools, they inappropriately transform competition law into ‘regulatory antitrust’. The present study challenges this view arguing that modern competition law intervention has moved beyond the crime-tort enforcement model and aspires to be ‘responsive’. This means that modern enforcers intervene ex ante and ex post, use prescriptive and proscriptive tools, and impose restorative and prophylactic remedies to ensure that the law is applied effectively. The works of the Greek Competition Authority offer a case study to illustrate this point. This authority has been utilizing a plurality of tools and enforcement strategies to enhance compliance and deterrence, and apply the law responsively. However, enforcement that aspires to be responsive may create problems of over-enforcement or under-enforcement, be vulnerable to regulatory failures or undermine Rule-of-Law principles. For this reason, this study draws on responsive regulation theory to make fourteen recommendations on how to address these challenges and ensure truly responsive enforcement.