This battle was the baptism by fire for this military unit, as well as for San Martín in the Spanish American wars of independence.

The battle started at dawn, when the grenadiers made a surprise pincer movement to trap the enemy forces.

[2] Montevideo organized a fleet to destroy the gun batteries at Rosario and Punta Gorda, two population centres along the Paraná, but were prevented from doing so as Buenos Aires dismantled them knowing that they could not be defended.

The Second Triumvirate promoted José de San Martín to colonel[4] and instructed him to follow them with the Regiment of Mounted Grenadiers and stop the raids.

[6] Those reinforcements included twenty-two rifleman, thirty cavalry, a small cannon and men armed with knives.

[7] Escalada arrived in San Lorenzo before the bulk of the patriot army, but the dust trail from the path to Rosario revealed their presence.

The Paraguayan disclosed the size of the royalist army and their plan of attacking the convent with a larger force, suspecting that the local money was kept in it.

[9] The battle was fought at the location of the modern city of San Lorenzo, Santa Fe which is next to the Paraná River, at the point of its widest flow.

[9] San Martín studied the battlefield and readied the plan for the operation during the night, when the grenadiers were hidden inside the convent.

The advantage of surprise and the speed of the cavalry charge allowed the regiment to defeat the larger royalist army who had almost double their number of soldiers.

[5] When Bermúdez and his column joined the battle the royalists were not able to stand their ground and were routed, retreating in disarray under covering fire from the ships.

[14] Despite the victory, the remaining royalist forces could not be pursued as the column led by Justo Bermúdez had moved further than calculated for.

This delayed the meeting with San Martín's column whose horse was killed by enemy fire, leaving with his leg trapped under the corpse of the animal.

A royalist, probably Zabala himself,[5][14] attempted to kill San Martín while he was trapped under his dead horse where he suffered a sabre injury to his face, and a bullet wound to his arm.

The exact moment this was said is unclear as the word after could have meant immediately after; during the ongoing battle; or some hours later during Cabral's agonising decline.

San Martín's report mentions him as "the grenadier Juan B. Cabral", and historians like Bartolomé Mitre, Herminio Gaitán, Gerardo Bra and Norberto Galasso support the idea.

[14] San Martín did not take hostages or ask for ransoms, but rather he instructed his people to avoid further conflicts and to try to restore peaceful relations with the royalists.

San Martín was aware that the new enlightened ideas at stake in the Napoleonic Wars influenced many of the Spanish military, and expected to convince Zabala that absolutism was a bad cause to defend.

[19] There are many Argentine memorials and places named after the battle, including three cities in Greater Rosario: Puerto General San Martín, Capitán Bermúdez and Granadero Baigorria are named after José de San Martín, Justo Germán Bermúdez and Juan Bautista Baigorria respectively, all of whom were involved in the battle.

The mayor of San Lorenzo, made an agreement with the Argentine Armed Forces in 2008 that the Regiment of Mounted Grenadiers would have a permanent presence at the site.

There is a monument with two symbolic wings of victory, an eternal flame and nine memorials for the 16 patriot soldiers who died in the battle.

The memorials are for the nine origins of those soldiers: the Argentine provinces of Corrientes, Santiago del Estero, La Rioja, Córdoba, San Luis and Buenos Aires, as well as Chile, France and Uruguay.

The military march was composed in February 1901 by Cayetano Alberto Silva following a proposal from Representative Celestino Pera.

However, the march includes a historical inaccuracy: "Here is the flag that one day in triumph rose over the battlefield and, full of pride and gallantry, to San Lorenzo led, inmortal."