Feng, seeing that Yuwen Huaji, who was repeatedly defeated by other rebel leaders, including Li Mi the Duke of Wei, Li Shentong (李神通) the cousin of Li Yuan (who, also in 618, established Tang Dynasty at Chang'an as its Emperor Gaozu), and Dou Jiande the Prince of Xia, was being weakened by the losses, befriended Yuwen Huaji's brother Yuwen Shiji, and suggested to Yuwen Shiji that he request permission from Yuwen Huaji to leave Liaocheng to collect food supplies for the army. Yuwen Huaji agreed, and Yuwen Shiji and Feng both left Liaocheng. After Liaocheng fell to Dou in 619, Yuwen Huaji was killed. Yuwen Shiji and Feng then fled to Tang territory. Emperor Gaozu, as he respected Feng as a Sui official, made him "Neishi Sheren" again, and soon promoted him to "Neishi Shilang" (內史侍郎), the deputy head of the legislative bureau. The chancellor Xiao Yu, impressed with Feng, recommended Feng, and Emperor Gaozu, in 620, made Feng "Zhongshu Ling" (中書令) -- a new title for the head of the legislative bureau, which Emperor Gaozu had changed the name of by this point to "Zhongshu Sheng" (中書省). As "Zhongshu Ling", Feng was considered a chancellor as well.