Amid deepening deglobalization， rising institutional heterogeneity， and intensifying geopolitical fragmentation， firms’ overseas supply chain governance faces a structural tension： openness is unavoidable， yet full openness is untenable. Existing studies largely treat deglobalization as an exogenous shock and emphasize defensive restructuring and risk mitigation， offering limited insight into how firms sustain control under conditions of continuing openness. Drawing on a longitudinal single-case study of Tsingshan Holding Group， a leading firm in China’s nickel value chain， it examined how firms construct a “controlled-openness” governance system for overseas supply chains. It identified three complementary mechanisms： the differentiated absorption mechanism enables market entry and local embedding by leveraging institutional differences； the hierarchical control mechanism maintains system sovereignty and operational control through the selective internalization of critical nodes； the rule coordination mechanism reduces dependence on any single institutional regime and enhances long-term predictability through rule alignment and collaborative rule-making. It further finds that these mechanisms do not evolve linearly； rather， they are selectively activated and combined in response to varying dimensions of structural tension， jointly supporting stable supply chain operations under high institutional uncertainty. From the perspective of organizational governance and tension management， it reveals how firms configure mechanisms to build structurally embedded control within persistent openness， offering an explanation for how openness and control can coexist in overseas supply chains under deglobalization.