神策军
Emperor Xianzong thereafter ordered a campaign against Chengde, and with the main imperial forces — the Shence Army (), commanded by the eunuch Tutu Chengcui — set to arrive in Weibo's vicinity, Tian was summoning his officers to discuss how to react — fearing that if the imperial forces were successful against Chengde, Weibo would be next. An officer stepped out and advocated a preemptive attack against the Shence Army, and Tian was ready to agree. However, at that time, Tan Zhong (), an emissary from Liu Ji the military governor of Lulong Circuit (盧龍, headquartered in Beijing), happened to be at Weibo, and he, trying to dissuade Tian from acting against imperial troops, pointing out if Weibo were in fact able to defeat the Shence Army, Emperor Xianzong would surely concentrate his attack on Weibo. Instead, Tan suggested, Weibo should enter into a secret agreement with Chengde whereas Weibo would launch a false attack on Chengde and capture a county to outwardly show Emperor Xianzong that he was not rebelling against imperial authority. Tian agreed with Tan, and in a pre-arranged attack captured Chengde's Tangyang County (堂陽, in modern Xingtai, Hebei).