A mobile ad hoc network is an infrastructureless multi-hop system of wireless autonomous mobile nodes. Reactive routing protocols like ad hoc on demand distance vector routing (AODV) and dynamic source routing (DSR) are appropriate for mobile environments, because they cope quickly with topological changes. Lately cooperative-transmission-based routing protocols have been proposed to further save energy and enhance reliability. However they require an existing conventional route and individual addressing of the cooperating nodes, which involves a lot of overhead. In this paper, we propose a new opportunistic large array (OLA)-based extension to AODV, which incorporates cooperative diversity into both route discovery and data transmission without requiring any pre-existing route or any individual addressing of relay nodes. An OLA is a form of cooperative diversity in which a group of simple, inexpensive relays or forwarding nodes operate without any mutual coordination, but naturally fire together in response to energy received from a single source or another OLA. Our proposed scheme inherits from OLA lower transmit energy and low computational overhead. However, this paper highlights a newly discovered feature of OLAs, which is robustness against mobility. We show through extensive simulation that this new technique yields significantly longer route lifetimes compared to the traditional AODV scheme, assuming node mobility according to the random waypoint mobility model. We also compare the end-to-end delays of the traditional and proposed schemes. To the best knowledge of the authors, this work is the only unicast, distributed, cooperative ad hoc routing scheme that does not require a pre-existing route.