In this letter, we propose a power-optimized NOMA with TXOP tuning based novel channel access scheme for IEEE 802.11ah dense IoT networks. Using the proposed method, we form the NOMA-clusters to mitigate the number of contending nodes in a group. Further, the proposed scheme enables nodes in a NOMA-cluster to transmit simultaneously using power-domain NOMA, as well as multiple frames based on the TXOP limit in single resource block. With an analytical model, we evaluate the throughput and connectivity performance. From the analytical and simulation results, it is evident that the proposed scheme significantly improve the performance of NOMA-IoT networks.