conservative nature of 802.11 ad hoc scheme has instigated extensive research whose goal is to improve spatial reuse and/or energy consumption of this scheme. Transmission power control (TPC) was shown to be effective in achieving this goal. Despite their demonstrated performance gains, previously proposed power-controlled channel access protocols often incur extra hardware cost (e.g., multiple transceivers). Furthermore, they do not fully exploit potential of power control due to heuristic nature of power allocation and interference margin computations. In this paper, we propose a distributed, single-channel MAC protocol (GMAC) that is inspired by game theory. In GMAC, multiple potential transmitters are first involved in an admission phase, which enables terminals to compute transmission powers that achieve a Nash equilibrium (NE) for given utility function. Subsequently, successful contenders can simultaneously proceed with their transmissions. Simulation results indicate that GMAC improves network throughput over 802.11 scheme by about 80%, and over another single-channel power-controlled MAC protocol (POWMAC) by about 40%. These gains are achieved at no extra energy cost.