Long-distance wireless local area networks (WLANs) are the key enablers of wide-area and low-cost access networks in rural areas. In a WLAN, the long propagation delay between an access point (AP) and stations (STAs) significantly degrades the throughput and creates a throughput imbalance because the delay causes unexpected frame collisions. This paper summarizes the problems caused in the medium access control (MAC) mechanism of the WLAN by a long propagation delay. We propose a MAC protocol for solving the delay-induced throughput degradation and the throughput imbalance between the uplink and the downlink in WLANs to address these problems. In the protocol, the AP extends NAV duration of CTS frame to protect an ACK frame and transmits its data frame to avoid delay induced frame collisions by piggybacking on the ACK frame transmission. We also provide a throughput model for the proposed protocol based on the Bianchi model. A numerical analysis using the proposed throughput model and simulation evaluation demonstrate that the proposed protocol increases the system throughput by 150% compared with that obtained using the conventional method, and the uplink throughput can be increased to the same level as the downlink throughput.