His efforts were swiftly crowned by success: the mountain Daylamites and the Gilites east of the Safid Rud river recognized him as their imam with the name of al-Nāṣir liʾl-Ḥaqq ("Defender of the True Faith") and were converted to his own branch of Zaydi Islam, which was named after him as the Nasiriyya and differed in some practices from the "mainstream" Qasimiyya branch adopted in Tabaristan following the teachings of Qasim ibn Ibrahim.

Although the Samanid force was far superior in numbers and equipment, Hasan managed to inflict a crushing defeat upon it in December 913 at Burdidah on the river Burrud west of Chalus.

A detachment that managed to find refuge in the fortress of Chalus was induced to surrender and then massacred by his son-in-law, Abu Muhammad al-Hasan ibn al-Qasim.

[2][5] Taking advantage of the murder of Ahmad ibn Ismai'il soon after, and the preoccupation of his successor Nasr II with cementing his own authority, Hasan was soon able to extend his control over all the old Zaydid domains, including both Tabaristan and Gurgan.

A Samanid counter-attack temporarily forced him to abandon Amul and withdraw to Chalus, but after 40 days he beat the invasion back and re-established his position.

[1][6] Hasan ruled over Tabaristan until his death in January/February 917, and even a Sunni historian like al-Tabari comments that "the people had not seen anything like the justice of al-Utrush, his good conduct, and his fulfilment of the right".

[1][5] His tomb in Amul became a major site of pilgrimage for the Daylamite and Gilite Shi'ites, and his descendants, who kept the honorific surname al-Nasir, were held in high esteem.