sentences:  Although Nguyễn Ánh immediately led a force northwards to Quy Nhơn in order to relieve Võ Tánh's besieged forces, the Nguyễn reinforcements could not break the Tây Sơn encirclement and a long battle resulted.Acknowledging the poor situation, Nguyễn Ánh ordered Võ Tánh to abandon the citadel, but Võ Tánh rejected and suggested that he would pin the main Tây Sơn force down there so that Nguyễn Ánh could attack their Citadel of Phú Xuân.Nguyễn Ánh agreed and then he attacked and captured Phú Xuân, forcing Tây Sơn emperor Quang Toan to flee to northern Vietnam.