This study presents a novel direct torque control (DTC) of permanent magnet (PM) brushless AC (BLAC) drive under single-phase open-circuit fault (SOF) accounting for the influences of inverter voltage drop (IVD), together with novel current model-based and voltage model-based stator flux estimation schemes for post-fault operation. It is demonstrated that for accurately elaborating the modified mathematical model, the voltage induced in the stator open phase winding and its relevant flux linkage should be taken into account although they do not contribute to torque production in the post-fault operating mode. It is also proven that reconfiguration of the conventional six-switch three-phase inverter for the purpose of faulttolerant control results in a significant magnitude imbalance between the α- and β-components of IVD. Thus, the influences of this unbalanced issue on performance of the two proposed stator flux estimation methods are investigated in details and a compensation method for the voltage model-based stator flux estimator is proposed and experimentally verified. It is shown that fault-tolerant control with high performance operation can be maintained for a DTC-based PM BLAC drive under SOF using the proposed modified mathematical model.