Tristán, in the meantime, had taken the time to fortify Portezuelo pass, the only access to the city through the hills from the southeast, a tactical advantage that supposedly would make the attempt impossible, except for the local area knowledge that the new conscripts brought to the rebels.

Captain Apolinario Saravia, a local from Salta, offered to guide the army through a high path that led to Chachapoyas, which would allow them to connect with the north road that went to Jujuy, in an area where there were no similar fortifications.

On February 18 they reached a field where they encamped, while the captain, disguised as a native wrangler guided a mule train loaded with firewood to the city, with the intention of reconnoitering the positions taken by Tristán's army.

The tactic was successful; columns of infantry under the command of Carlos Forest, Francisco Pico and José Superí broke the enemy lines and entered the city streets, closing the royalist retreat on the center.

The generosity of Belgrano, who embraced Tristán and allowed him to keep his command symbols – they were personal friends, having been classmates at the University of Salamanca, been roommates in Madrid and loved the same woman[3] – would cause surprise in Buenos Aires, but the decisive victory silenced the critics and earned him a prize of 40,000 pesos granted by the Assembly.

Governor Feliciano Chiclana placed a wooden cross on the common grave where the 480 royalist and 103 independentist troops were buried with the inscription "A los vencedores y vencidos" (To the victors and the vanquished).