This paper investigates to what extent internal R&D efforts and different types of external knowledge sources jointly affect innovation performance of firms in emerging economies. Based on a survey about external knowledge sourcing activities of Chinese innovative firms, we categorize external knowledge sources into four groups: science-based partners; horizontal connections; value chain partners, and technology service providers. We find that both internal R&D activities and external knowledge sourcing have a positive effect on firms' innovation performance. Strong internal R&D capabilities also increase the effect of sourcing from value chain partners and horizontal connections, but we do not find support for complementarity between internal R&D and collaborations with universities and research labs. These findings jointly suggest that the mixture of different types of external knowledge partners in combination with internal R&D capabilities is crucial in understanding the role of open innovation in emerging economies.