In mid January, after the combat with the Anglo-French squadron twice at The Vuelta de Obligado, Lucio Norberto Mansilla general placed eight guns hidden under brush piles, 250 carabineers and 100 infantryman in the ravines of the coast between the convent of San Lorenzo and the point of Quebracho

At noon on January 16 appeared the British steamship HMS "Gorgon", the French corvette expeditive, the brigantines HMS "Dolphin", "King" and two armed schooners in Colonia del Sacramento, which were 37 heavy guns and accompanied by 52 merchantmen gunships.

When faced the town of San Lorenzo, the Gorgon and the expeditive made ​​three shots of bullets and shrapnel onto the coast to discover the strength of Mansilla. The Argentine soldiers remained hidden in their post, according to the order received. When all the convoy was at the narrows of the river where is pronounced upstream from San Lorenzo, Mansilla ordered the fire of break up his batteries led by the Captains Joseph Serezo, Santiago Maurice and the Navy Lieutenant Colonel Alvaro de Alzogaray. The attack was accurate; the merchant ships dismantled, laid course toward two nearby streams, increasing with the collision between one another the breakdowns that made them the  land cannons.

At four in the afternoon, the fighting continued tough yet, and the convoy was not worth his steps with great damage. Favoured by the aft wind and after the vessels which constantly were vomiting a deadly fire, the invader convoy approached the Quebracho.

Here there were reconcentrated his forces Mansilla, where he continued fighting until nightfall, when they dismounted their guns and neutralized their rifle fires by the enemy cannon, the convoy was able to save the tip of Quebracho, with great damage to warships, considerable losses in manufacturing and 50 men out of combat.

The British Admiral Inglefield, in his official report to the British Admiralty said that "the English and French steamers held fire for over three and a half hours, and only one ship in the convoy left without being shot."

The Argentines loss this time was negligible, and Mansilla could properly say that "it was his turn to defend the honor of the flag of his country on the same site of San Lorenzo that with his blood San Martin watered to drive the first charge of its later famous Horse Grenadiers. "

The Hit & Run tactic in San Lorenzo:

The British commander of the HMS Philomel described the Argentine attack in San Lorenzo:

"Mansilla had prepared all his forces to attack the convoy and knowing now that the battery stationary would not work, since we would locate those, adopted a more cunning plan: to use mobile artillery. It was about twelve field guns large caliber and about two thousand men on the cliffs of San Lorenzo which are about 4 miles long and seventy feet high (7.5 kilometers and 21 meters high above the river ). The boats had to pass within a quarter mile (450 meters) from the cliffs. The terrain was flat and could not see anything except from the river cliff so that his men were safe from the fire of our ships.

Sixty vessels approached. The HMS Dolphin led the first division of the convoy, Key's HMS Fanny in the following division and Hope's covering their rear.

The Argentine arms kept coming to the cliff showing only their mouths, and retreated firing, loaded again and reappeared in a new place. Thus cannonaded the convoy for three hours each ship are impacting several times. One of the merchant brigantines had 34 impacts. The HMS Firebrand suffered 22 impacts, four through their chimney. Thanks to Providence do not died no one of crews of the 60 vessels in the HMS Firebrand and there were only two wounded.

The enemy artillery handled so well that it was almost impossible to locate them  with our fire. The muzzle of their guns was evident only for a moment and immediately moved so that before we prepared our guns and fired them had already disappeared. The HMS Dolphin and HMS Fanny fired fifty shots like the French corvette Coquette but they did not cause any damage to the enemy.

The enemy fired and admirably handled their artillery guns as the best in the world. Among our vessels had been many American ships. More than 60 allies were wounded or killed. Several ships were hit, including the British Caledonia barge with goods valued at 100,000 pesos, part of which was saved when the troops of Mansilla extinguished the fire aboard a small schooner. "

Navy Lieutenant Colonel Juan Bautista Thorne, 2nd Commander of Mansilla was badly wounded in his shoulder. At sunset the people of Rosario observed fleeing the Anglo-French fleet. The HMS Firebrand stopped and disembarked two of his men who had been severely wounded in Vuelta de Obligado. British surgeons had to amputate one of his legs. the Actions in San Lorenzo.

The Tonelero and the Angostura of the Quebracho placed an end to foreign navigation through our rivers. Never again was to be repeated a convoy of eight months duration.