Small and medium-sized enterprises (SMEs) increasingly operate within digital ecosystems where decision-making is mediated by external platforms, data infrastructures, and algorithmic tools. Under these conditions, managerial choice is shaped not only by internal capabilities, but also by ecosystem-level governance, information thresholds, and feedback mechanisms. This paper develops a theory-building analysis of decision-making under digital ecosystem conditions, using professional football clubs as a paradigmatic case of decision-intensive SMEs operating in data-rich, platform-mediated environments. Through a structured synthesis of the scientific literature, the study introduces the concept of Ecosystem-Mediated Decision Control (EMDC), which conceptualizes decision-making as a closed loop linking data inputs, algorithmic mediation, managerial judgment, and organizational feedback. The analysis demonstrates that artificial intelligence does not replace managerial agency, but restructures decision control by redistributing informational authority within the ecosystem. By articulating four decision dynamics—decision mode variability, information threshold effects, oscillatory human–algorithm control, and feedback-based decision stabilization—the paper offers a transferable explanatory framework for SMEs operating in digital ecosystems. The findings contribute to the literature on digital ecosystem economics by clarifying how decision authority, adaptability, and learning emerge under platform-mediated conditions.