While it is widely acknowledged that conditionality has been used to install competition governance in economies in transition, little is known about how the European Union and the United States of America project their competition preferences to emerging markets and to what extent the EU and the US approaches have been conditioned by domestic factors in target jurisdictions. This article, drawing on theoretical concepts of external governance and policy diffusion, compares the horizontal engagement approaches of the EU and the US in the permeation of competition law and policy to Brazil and China. It argues that while engagement and market-based approaches are more reliant on domestic demand and a willingness to engage than hierarchical forms of interaction, a more institutionalized and constraining effort is more resilient to political interests. Norm deviation from expected convergence incurs measures of higher level of constriction.