While the Arab army demobilized and returned to their homes for winter, the Türgesh ruler Suluk, now advised by Ibn Surayj, launched an invasion of Lower Tokharistan.

This unexpected victory shored up the threatened Umayyad position in Khurasan, while diminishing the prestige of Suluk, who fell victim to inter-Türgesh rivalries in early 738.

[1] The loyalty of Transoxiana's native Iranian and Turkic populations to the Umayyads remained questionable, however, and in 719 the various Transoxianian princes sent a petition to the Chinese court and their Türgesh vassals for military aid against the caliphate's governors.

The Umayyad governors initially managed to suppress the unrest, but control over the Ferghana Valley was lost and in 724 the Arabs suffered a major disaster (the "Day of Thirst") while trying to recapture it.

[11][12][13] The campaign had been a disaster for Asad and his now mainly Syrian army; Umayyad control north of the Oxus had collapsed entirely, and while the governor had been able to escape complete destruction, he had suffered considerable casualties.

On Ibn Surayj's urging, on the other hand, the Türgesh khagan decided to launch a winter attack into Lower Tokharistan, hoping to raise the local population in revolt against the Umayyads.

Asad initially refused to call upon the help of the local Khurasani Arabs, indicating the level of mistrust existing by now between the latter and the representatives of the Umayyad regime; in the end, however, he relented, and gathered a force of 7,000 men.

[21][22] The account in al-Tabari of the ensuing battle is confused and, according to the Orientalist H. A. R. Gibb, "shows the marks of rehandling", but it appears that Asad managed to surprise the Türgesh ruler and Ibn Surayj near Kharistan.

Mansur al-Bajali commanded the vanguard as before, reinforced by the troops of the district of Damascus (under Hamlah ibn Nu'aym al-Kalbi) and the personal retinue of Asad.

[26] The khagan, who had only 4,000 of his men with him, placed Ibn Surayj and his followers on the right, while the rest of his force consisted of his Türgesh and of contingents from the princes of Transoxiana—al-Tabari implies they were there in person, but this is unlikely—including the rulers of Sughd, Shash (Tashkent), Usrushana, Khuttal, and the Yabghu of Tokharistan.

Suluk fled before the Umayyad pursuit, but the Arabs were soon hampered by heavy rain and snow, allowing the khagan and Ibn Surayj to escape to Upper Tokharistan, whence they moved on to Usrushana.

[...] Kharistan was not only the turning point in the fortunes of the Arabs in Central Asia, but gave the signal for the downfall of the Turgesh power, which was bound up with the personal prestige of [Suluk]."

Conversely the defeat diminished the prestige of Suluk, and may possibly have played a role in his assassination early in 738, although rivalries between the Türgesh, fanned by the Chinese court, were more directly responsible for this.

[32][33][34] Under Asad's successor, Nasr ibn Sayyar, the Umayyad armies recovered most of Transoxiana by c. 743, and with the Battle of Talas in 751 and the turmoil of the An Shi Rebellion, which terminated Chinese influence in Central Asia, Muslim dominance in the region was secured.