In this battle, the Chilean cavalry led by Lieutenant Colonel José Francisco Vergara and Sofanor Parra ambush and massacre the allied cavalry commanded by Peruvian Lieutenant Colonel José Buenaventura Sepúlveda who was in the rear of the allied army, which had already undertaken their march to Dolores, in the Pampa Germania sector, near Agua Santa.

The day after the Chilean landing in Pisagua, the Lieutenant Colonel of the Chilean National Guard Don José Francisco Vergara was sent, along with five officers to San Roberto, since there was news that an allied contingent of about 6,000 soldiers was concentrated there,[4] but they returned without finding anything.

Upon his return, Vergara suggested to General Erasmo Escala to carry out a major reconnaissance in the area,[5] for which an exploration party was sent to the desert in order to verify the Allied withdrawal and establish security and water supply zones for the rest of the troops.

Juan Buendía had ordered to gather the allied troops in Agua Santa after the Chilean landing, while he was heading towards Pozo Almonte.

Records from Chilean historiography recounts that both forces were arranged in line to charge and that when both collided, the Chilean cavalry, on higher mounts and in numerical superiority, broke the center of the allied forces, separating the Peruvian horsemen in a direction to the north and north while the Bolivians to the south.