Designing high-speed, energy-efficient heterogeneous wireless networks has recently emerged as a key research challenge. A novel approach for radio resource management at the base station (BS) level is introduced with the objective of improving the spectral-efficiency, while keeping the energy-efficiency (EE) at an acceptable level. In this paper, a hybrid opportunistic ON/OFF switching (OOFS) and dynamic channel allocation (DCA) mechanism is proposed. The problem is formulated as a non-cooperative game between the BSs who seek to decide on their transmission mode and channel allocation parameters. To solve this game, a two-step algorithm is proposed. At first, a mixed-strategy game is used, so the BSs may decide independently about their power management strategy. In the second step, the BS selects its downlink channel using a fully distributed channel segregation approach. In dense heterogeneous environments, the DCA algorithm shows a significant improvement in terms of BS throughput over OOFS algorithm, while keeping an acceptable EE level comparable to OOFS.