Innovation ecosystems are increasingly regarded as important vehicles to create and capture value from complex value propositions. While current literature assumes these value propositions can be known ex-ante and an appropriate ecosystem design derived from them, we focus instead on generative technological innovations that enable an unbounded range of potential value propositions, hence offering no clear guidance to firms. To illustrate our arguments, we inductively study two organizations, each attempting to create two novel ecosystems around new technological enablers deep in their industry architecture. We highlight how ecosystem creation in such conditions is a systemic process driven by coupled feedback loops, which organizations must try to control dynamically: firms first make the switch to creating the ecosystem following an external pull to narrow down the range of potential applications; then need to learn to keep up with ecosystem dynamics by roadmapping and preempting, while simultaneously enacting resonance. Dynamic control further entails counteracting the drifting away of the nascent ecosystem from the firm's idea of future value creation and the sliding of its intended control points for value capture. Our findings shed new light on strategy and control in emerging ecosystems, and provide guidance to managers on playing the ecosystem game.