The self-organizing nature of ad hoc networks is a good aspect in that terminals are not dependent on any infrastructure, that is, networks can be formed with decentralized and autonomous manner according to communication demand. However, this characteristic might affect the performance in terms of stability, reliability and so forth. Moreover, ad hoc networks face a scalability problem, which arise when the number of terminals in a network increases or a physical network domain expands, due to the network capacity limitation caused by the decentralized and the autonomous manner. Regarding this problem, some hierarchical and cluster-based routings have been proposed to effectively manage the networks. In this paper, we apply the concept of hierarchical routing and clustering to opportunistic routing, which can forward packets without using any pre-established path to achieve a path diversity gain with greater reachability. The simulation results show that the proposed method can achieve 11% higher reliability with a reasonable end-to-end delay in dense environments and 30% higher in large-scale networks.