This meant little in practice, as neither the Abbasid government nor Ibn Kundaj possessed the force to wrest Ibn Tulun's territories from him, but, along with his appointment to command the Caliph's private guard (), it made Ibn Kundaj nominally one of the most powerful men of the Caliphate. Ibn Tulun's death in 884 seemed to present an opportunity to capture some of his territories in Syria from his inexperienced son and heir, Khumarawayh. Ibn Kundaj allied himself with the Abbasid general Ibn Abu'l-Saj, and received authorization and some troops from al-Muwaffaq. Ibn Kundaj clashed with the Tulunid governor of Raqqa in April 884, and soon after, the Tulunid governor of Damascus defected, bringing with him Antioch, Aleppo and Hims. Khumarawayh responded by sending troops to Syria, who soon succeeded in recovering the lost cities, before both sides settled into winter quarters. In the spring, al-Muwaffaq's son, Abu'l-Abbas Ahmad (the future Caliph al-Mu'tadid), arrived to take control. Ahmad and Ibn Kundaj defeated the Tulunids, who were driven back to Palestine, but Ahmad quarrelled with Ibn Kundaj and Ibn Abu'l-Saj, who departed with their troops, and at the Battle of the Mills on 6 April Khumarawayh's general Sa'd al-Aysar routed the Abbasid army. This signalled the end of the alliance between Ibn Kundaj and Ibn Abu'l-Saj: the latter now turned to Khumarawayh, and persuaded him to invade the Jazira. With Egyptian aid, Ibn Abu'l-Saj crossed the Euphrates, defeated Ibn Kundaj's forces in a number of battles in 886–887, and forced him to recognize Tulunid control. The entire Jazira now became a Tulunid province, a fact recognized by the Abbasid government in a treaty in the December 886 that confirmed Khumarawayh in his old and new possessions. Ibn Kundaj remained as governor of Mosul under Tulunid authority. In 887/8 he tried to rebel but was defeated. Although he re-acknowledged Tulunid suzerainty, he was now stripped of Mosul in favour of Ibn Abu'l-Saj. Ibn Kundaj now concentrated his attentions on defeating his rival, and soon managed to secure the favour and support of Khumarawayh: in 888–889, it was Ibn Kundaj who, at the head of a Tulunid army, defeated and ousted Ibn Abu'l-Saj, who fled to al-Muwaffaq.