Purpose - This paper aims to investigate the effect of specific subsets of digital technologies and governance mechanisms (i.e. relational and contractual) on the efficiency of the automotive supply chain (SC). Design/methodology/approach - Building on the Transaction Costs Economic (TCE) theory, and on the literatures on the governance and Digital Transformation of SCs, the research employs a multi-respondent survey on a sample of 101 Italian automotive suppliers. It analyses the interplay between investments in network and physical-digital interface technologies and buyer-supplier relationship governance models in a joint product development effort. The related effects on costs, from the automotive suppliers' perspective, are considered. Findings - The results confirm the TCE assumptions on governance mechanisms being appropriate to enhance cost performance, but in particular show that digital technologies shape the governance of buyersupplier relationships with different patterns. The features of synchronisation and accessibility, as ensured by network technologies, are found to strengthen the impact of contractual governance, while the adoption of physical-digital interface technologies, and their enhanced features of virtualisation and traceability, further enhance the impact of relational governance on the efficiency improvements of suppliers. Originality/value - This study is one of the first to have considered Digital Transformation in SCs from the suppliers' perspective and its implications on the efficiency of relationship governance with buyers.