In 398, Duan Ye sent Juqu Mengxun to attack Xi Commandery (), in modern Zhangye, Gansu), and Juqu Mengxun captured it and its governor, Lü Guang's nephew Lü Chun (). Soon thereafter, Jiuquan (酒泉, roughly modern Jiuquan, Gansu) and Dunhuang (敦煌, roughly modern Dunhuang, Gansu) Commanderies submitted as well, allowing Northern Liang to take over a large portion of formerly Later Liang territory. Lü Guang's son Lü Hong () then also withdrew from Zhangye (張掖, in modern Zhangye), and Duan Ye moved his capital from Jiankang to Zhangye to further pressure Later Liang. He trailed Lü Hong to try to attack him, against Juqu Mengxun's advice not to cut off Lü Hong's escape, and was defeated by Lü Hong, saved from destruction only by Juqu Mengxun.