Within the 5th Division was the Vanguardia Sniper Mobilized Squad, a cavalry unit made up of horsemen from Cotagaiteños, Tupiceños and Tarijeños, under the command of Colonel Rufino Carrasco.

On December 3, a 3-man Chilean picket ran into Carrasco's forces; one was killed, another captured and the other managed to flee, giving the alarm to Commander Barboza.

Lieutenant Emilio Ferreira, commander of the Chilean garrison of San Pedro de Atacama, as soon as he received the message from his soldier, he deployed his 23 men in the Tambillo gorge, a league and a half north of the town.

The battle began in the early hours of the 6th, as soon as the Chileans, sheltered behind some stone walls, spotted the opposing forces and opened fire on them.

After the combat, Carrasco's forces occupied the town, immediately requesting General Campero to send reinforcements to hold their position.

The news of this confrontation caused a commotion in the Chilean forces occupying Antofagasta, as they believed that it could be the appearance of the vanguards of the 5th Division of Campero, announced so many times in march on the coast, a campaign that was never carried out.