In fall 763, Emperor Daizong faced two new additional threats. Pugu, whom two other generals Xin Yunjing () and Li Baoyu and the eunuch Luo Fengxian () had suspected of plotting rebellion, was angry at the suspicion on him and, after submitting a number of accusatory petitions, began to act independently of the imperial government. Meanwhile, though, Tibet, which had begun to seize Tang western prefectures one by one during the Anshi Rebellion, launched a sudden attack on Chang'an. At that time, with Cheng in power and the generals hating him for his previous accusations against the generals Lai Tian () and Li Huairang () that led to their deaths, when Emperor Daizong sought emergency aid from the provincial generals, none came to his aid, and on November 16, he was forced to abandon Chang'an and flee to Shan Prefecture (i.e., Shancheng). Tibetan forces declared Emperor Suzong's cousin Li Chenghong the Prince of Guangwu the Emperor of Tang, although they withdrew within the course of a month due to the Tang people's resistance efforts and counterattacks commanded by Guo Ziyi. Emperor Daizong was able to soon return to Chang'an. Still, much territory had fallen into Tibetan hands and Tang forces were not able to counterattack. As the popular sentiment at the time blamed Cheng for the disaster, he stripped Cheng of his posts and sent him back to his home. Soon thereafter, the most powerful figures at court became the chancellor Yuan Zai, who flattered Emperor Daizong, and the eunuch Yu Chao'en, who commanded the imperial guards.