In the next year, he was dispatched to conquer Champa. He demanded from Đại Việt (mordern Vietnam) a route to Champa, which would trap the Champan army from both north and south, but it was rejected by retired emperor Trần Thánh Tông, whom was the "de facto" ruler of Đại Việt. As a result, Toghon decided to attack Đại Việt. At first he won several victories and captured Thăng Long, the capital of Đại Việt. Trần Thánh Tông had to offer princess An Tư to him to slow down the pace of the Mongol army. Later he was defeated by Trần Hưng Đạo and fled back to Huguang province.