The advent of the digital economy and, implicitly, of competition in the online marketplace has triggered new challenges in terms of consumer protection approaches. Online, consumer skills are expected to be improved and the level of consumer awareness and engagement increased. These are the baseline prerequisites of the sustainable purchasing decision and, thus, should be considered as pillars of responsible online consumption. Consistent with the novel consumption challenges, the current paper is intended to advance and test a research model integrating five main constructs, namely, competition in the online marketplace, online consumer skills, online consumer awareness, online consumer engagement and sustainable purchasing decision. A total of 318 college students—a representative population of the new Millennials generation—accepted the invitation to participate in a questionnaire-based survey. In order to pertinently analyze the collected data, a structural equation modeling technique based on partial least squares was employed for the assessment of the measurement and the structural model. The findings indicated that the model explained 24.4 percent of the variance of sustainable purchasing decisions, while the highest influence was exerted by the improvement of online consumer skills. This implies that online providers should revisit their products sustainability standards on purpose to preserve a competitive advantage.