Under the “One Country, Two Systems” rule, Hong Kong and China maintain different legal systems. This dichotomy applies also in antitrust: China adopted its Anti-Monopoly Law in 2007, while Hong Kong waited until 2012 to introduce its Competition Ordinance (and another three years to fully implement it). This article compares the antitrust laws of these two jurisdictions, and their enforcement, in the light of a turning point: the disruption caused by so-called Big Tech. Interestingly, while the competition laws of Hong Kong and China are substantively similar to each other and to legal precedent in other jurisdictions, Hong Kong has adopted an adversarial system of enforcement, and China an administrative system. Through an analysis of recent antitrust developments in the two jurisdictions, this article shows the importance of agency independence, due process, and robust judicial scrutiny for the proper functioning of an administrative system of enforcement; and at the same that judicial scrutiny in an adversarial system needs the certainty of legal rules, in particular to clarify the burden of proof to be met by the competition authorities. In the light of these findings, this article proposes that the two principles of due process and robust but workable judicial scrutiny should remain at the heart of antitrust. This is important at a time when, globally, the frustration with market concentration in certain sectors, and especially with Big Tech, may lead policymakers to propose changes to antitrust enforcement that could weaken these two principles, and to attribute higher value to the speed of decision-making, over the importance of a thorough analysis.