The analysis of tourism supply chains has traditionally focused on the two-party relationships between vertical suppliers. However, since a full supply chain is composed of horizontal, vertical and diagonal suppliers, there is a gap in literature regarding the dynamics of how these triadic relationships operate within a tourism supply chain. Using a multiple case study design involving four tour operators in Macau, this paper explores the interplay of relationships among horizontal, vertical and diagonal suppliers. We capture the evolutionary dynamics of how coopetitive relationships are formed between horizontal suppliers, the subsequent impact on both vertical and diagonal suppliers, and the resulting overall changes in the structure of the tourism supply chain. This paper contributes to tourism supply chain literature through a coopetitive lens by analyzing the triadic relational links among horizontal, vertical and diagonal suppliers.