In the late 1310s Castile was ruled by King Alfonso XI, a minor, under the joint regency of his grandmother Maria de Molina, of his granduncle infante John and of his uncle infante Peter. An agreement had been reached for a new expedition to begin in the late spring of 1319. This expedition was to be a large one, blessed by Pope John XXII who authorized it as a crusade.

The troops assembled in Cordoba in June 1319 and crossed the border under the command of infante Peter. With him were the Grand Masters of the Orders of Santiago, Calatrava and Alcántara and the Archbishops of Toledo and Seville.

A siege of the city of Granada was deemed impossible at the time. The withdrawal started on 25 June 1319, in very hot weather; infante Peter led the vanguard while infante John commanded the rearguard.

At this point Sultan Ismail decided to strike. A large force of elite Moorish cavalry, the "Volunteers of the Faith", led by Uthman ibn Abi al-Ula, exited from Granada and started harassing the retreating Castilians of infante John. These minor attacks turned into a general assault when the Granadines realized the Castilians were losing their cohesion during their retreat and were unable to fight back effectively. At this point the vanguard thought only of flight and to reach the Castilian border; in their panic, many men drowned while attempting to cross the river Genil in full armour. The unsupported rearguard collapsed, with infante John falling victim probably to stroke or heat stroke leading to a spectacular Moorish victory.