In the town of San Jerónimo, Huarochirí Province would the Breña campaign begin with the forces under Colonel José Agustín Bedoya confronting those of Alcérreca with the latter attempting to capture in the city by the front but would be repulsed by the Peruvians through the stone walls in the town's vicinity. This would leave three Chileans killed and six wounded.[2]
The next day, Major Cámus would reinforce Alcérreca with 100 soldiers as they were dispatched via train from Chosica to San Jerónimo where eight wounded from the battle would also arrive. On April 11 at 7:20 PM would Alcérreca request a further 75 soldiers which would be commanded by Colonel Adolfo Silva Vergara while simotaniously request information about their respective soldiers and the Peruvian forces. He would obtain his response by 8:45 PM that the Chileans had received three more wounded and the Peruvians had suffered enough casualties to withdraw from the town.[3] A few moments later, Alcérreca would later announce that he had occupied the town with the following:
The Buin retook the hills, and at four in the afternoon entered San Jerónimo, news that reached the camp by light of the fire in the town. At eight o'clock at night, thirty carabinieri, crossing the rapid current of the Rimac, transported the rump to the opposite bank as many infantrymen who flanked the enemy position on the right side. A new flare communicated that the town of Cayaguanca had been occupied in turn (...) Around San Jerónimo there are four towns: Chacle, Cayata, Quiromarca and Quilmachai (...) The montoneros dispersed towards all these points, that they are all neighbors or compadres of these places.[4]
Faced with this predicament, Silva Vergara ordered the town to be razed and retreat back to Chosica. On April 12 and at 3 PM, the Chileans would abandon the place "after punishing the civilians of San Jerónimo, Cayagance, Santa Eulalia and the valley in between" according to Alcérreca's report.[3]