This paper proposes a fault-tolerant MTPA control method for permanent magnet synchronous machine (PMSM) drives under one-phase open-circuit fault. The proposed method isolates the open-circuit faulted phase after the fault and the motor starts to operate as a two-phase machine fed by an H-bridge inverter. Neither an additional inverter leg nor a neutral-point access to stator or DC link is used for the speed control. This post-fault configuration enables the motor to operate in a wider range of speed even than the healthy system, despite the reduced power devices, drivers and current sensors. The behavior of the faulted system is analyzed with a modified d-q model. Based on the analytic results, a speed control algorithm is developed. The strategy includes a maximum torque per ampere (MTPA) control to improve the drive efficiency and a flux-weakening control to maximize the feasible inverter output voltage within the limit. The proposed control method is verified by experimental results.