Improving the network throughput is a primary objective in mobile ad hoc networks (MANETs), which is motivated by the over-conservative nature of the 802.11 standard. Transmission power control (TPC) was proposed for improving spatial reuse and reducing energy consumption in MANETs. Previous TPC protocols either incur extra hardware cost (e.g., require multiple transceivers) or do not fully exploit the potential of power control. In this work, we propose distributed, single-channel MAC protocols for MANETs that exploit TPC and account for different packet sizes in the system to further maximize spatial reuse. We model channel contention in the network as a non-cooperative game. Multiple potential transmitters are first involved in an admission phase which enables terminals to compute the transmission powers that achieve a Nash equilibrium (NE) for a given utility function. Subsequently, successful contenders in the same neighborhood can simultaneously proceed with their transmissions. Simulation results show that our protocols significantly improve the network throughput (in terms of transmitted bits/second or the number of admitted contenders) over previously proposed schemes. Our results also indicate that these gains do not require additional energy cost.