The “fuzzy front-end” (FFE) of innovation begins when an opportunity is first considered worthy of further ideation, exploration, and assessment and ends when a firm decides to invest in or to terminate the idea (Khurana & Rosenthal, 1998). Since such an early phase is often characterised as being highly uncertain and unstructured, scholars have suggested that uncertainty must be reduced as much as possible during the FFE to achieve success in innovation (Frishammar et al., 2011; Moenaert et al., 1995; Verworn, 2009; Verworn et al., 2008). Although openness has been proposed as crucial to innovation success (Chesbrough, 2003; Chesbrough et al., 2006), little effort has been put into studying its role in reducing uncertainty in the FFE of service innovation. To address this gap, the current study aims to examine the effect of “openness competence” within the FFE – i.e., the ability of a FFE team to explore, gather and assimilate operant resources from external sources by means of external searches and inter-organisational partnerships – on the success of service innovation. It will also identify the key dimensions of openness competence. This mixed methods study is comprised of two main phases. In the first phase, we interviewed 12 informants who participated in the FFE of 6 distinctive online service innovations. The data were analysed through a services-dominant (S-D) logic analytical lens. The case findings together with the extant literature were used to develop a formative second-order construct of openness competence, and to form a series of hypotheses concerning an “open service innovation” (OSI) model. In the second phase, a total of 122 valid survey responses were collected and analysed using a partial least square structural equation modelling (PLS-SEM) technique with the aim of validating the proposed OSI model. The key findings of this study include the four dimensions of openness competence within the FFE, namely: searching capability, coordination capability, collective mind and absorptive capacity. A FFE team’s IT capability was identified as an antecedent of openness competence. Further, we found that openness competence is positively associated with the amount of market and technical uncertainty being reduced during the FFE. Contrary to our expectations, the impact of openness competence on service innovation success is direct, rather than being mediated by the degree of uncertainty reduction. These findings offer several implications for research on open innovation and on the FFE. Additionally, by identifying the key dimensions of openness competence, the current study provides guidance to front-end managers as well as presenting new areas for future research.