Socio-technical regimes are highly institutionalized rationalities that have co-evolved with actors, technologies and institutions over extended periods of time and become taken for granted across geographical contexts. Transition studies feature an extensive focus on regime dynamics within specific territorial contexts. However, we know surprisingly little of how regime rationalities are constructed, diffused and reproduced across space. This is a key gap in the geography of sustainability transitions literature. This paper introduces a conceptual model to analyze transformative opportunities in regions and how regime actors strategically diffuse and implement global regime solutions through combinations of discursive and substantive system reconfiguration activities. The empirical analysis draws upon a combination of Socio-Technical Configuration Analysis (STCA) of 354 newspaper articles and 10 in-depth expert interviews to illuminate how regime actors prevailed in diffusing and legitimizing the water sector's dominant socio-technical configuration in San Diego during a period of substantial transformative opportunities.