The night was intensely dark, and the streets of the village were very narrow, cut into gullies and very muddy. A heavy rain was pouring down, and the march was made under difficulties and necessarily slow. General Smith's position was on an eminence about one thousand yards from the enemy's works, from which point he made the attack. Riley moved up the ravine to a slope leading to a high point of the ridge and attacked the enemy some eight hundred yards distant. Cadwallader followed Riley, and the Mounted Rifles and Engineer Company moved to a position in rear of the force confronting Riley. The Third Infantry and First Artillery were held in reserve. The attack was made as ordered by General Smith, and the enemy fled, pursued by Riley, the Mounted Rifles, and Engineers.

The Third Infantry and First Artillery, held in reserve, were attacked by a force of cavalry, which was driven off, and Valencia was completely routed. General Shields, who held the village, seized the main road and cut off retreat in that direction. The enemy fled in the greatest confusion. The battle of Contreras was one of the most brilliant victories of the war. It opened the road to the City of Mexico. Seven hundred of the enemy were killed, eight hundred and thirteen prisoners were captured, including eighty-eight officers, of whom four were generals; many standards, twenty-two pieces of brass cannon, a large number of stands of small arms, seven hundred pack mules, many horses, and large quantities of ordnance stores were added to the outfit of the American army.

General Scott had planned to open up the way for the march of his army to the City of Mexico by the way of Padierna. Knowing or believing that a stubborn defense would be made by the Mexicans, he had ordered General Worth to march from San Antonio on the morning of August 20th, with Garland's brigade, by way of San Augustin to Padierna, to be followed by General Quitman, who was ordered to leave a cavalry force to hold San Antonio. But General Persifor F. Smith had won the battle before these troops arrived.

A sufficient guard having been left with the prisoners, General Persifor F. Smith was ordered with his brigade, the Mounted Rifles and Engineers, in pursuit of the fleeing enemy. They were attacked at San Angel, but the attacking party were soon driven off. General Pillow joined these forces at San Angel, and General Scott came up with them at Coyoacan, where he had ordered the army to halt.

From this point in the direction of the capital, Churubusco was one mile; two miles to the southeast was San Antonio. Churubusco is about six miles south of the City of Mexico, on a river of the same name, and on the road from San Angel and San Antonio from San Augustin. General Scott on his arrival ordered Captain Lee, with Captain Phil Kearney's company of the First Dragoons and a company of the Mounted Rifles, to make a reconnoissance. In the meantime Pillow and Cadwallader were to attack San Antonio in the rear, General Worth assailing it in front. A reconnoissance having been made of the convent of San Pablo, in the town of Churubusco, a brigade from Twiggs's division, a part of Smith's brigade, Riley's brigade, and Taylor's battery were ordered to attack. After the defeat of General Valencia at Contreras, General Worth returned with Garland's brigade in front of San Antonio. His orders were to attack as soon as Pillow and Twiggs, moving from Contreras, approached in the rear. Worth ordered Clarke's brigade to move over the pedregal and turn the right flank of the fortifications at San Antonio and cut the enemy's line of communication. Henry Francis Clarke's brigade was attacked on its march, but dispersed the attacking force, and soon encountered the rear of the Mexicans from San Antonio and engaged them. Pillow with Cadwallader's brigade, joined Worth in pursuit of the fleeing Mexican troops and both attacked the tête-de-pont in their front. Riley's brigade having been ordered forward, General Scott ordered Pierce's brigade to move by the road leading north from Coyoacan across the Churubusco River by a bridge, turn to the right, and seize the causeway in the rear of the tête-de-pont. General Scott, learning that General Shields, in the rear of the Mexican lines, was in danger of being cut off and captured, ordered Major E.V. Sumner with the Mounted Rifles under Major W.W. Loring, and the Second Dragoons under Captain Henry Hastings Sibley, to his support. The attack of the Americans being persistently pressed on all sides, the Mexicans gave way and made a precipitous retreat, pursued by the victorious Americans.

There remained yet to be captured the convent of San Pablo. This building, having very thick walls, was impervious to the attack of field pieces. It was defended by a well-constructed bastion, with flooded ditches, and guns placed in the embrasure. The attack was made by the First Artillery, followed by the Third Infantry. During the attack the enemy made several sallies from the convent, which were repulsed. The troops in the convent consisted of the Independencia and Bravo battalions, about six hundred and fifty each, with the necessary cannoneers for six guns, and in the tête-de-pont cannoneers for five guns, the San Patricio companies, and the battalion of Tlapa. Along the Rio Churubusco, on the north side, was the brigade of General Perez, some twenty-five hundred strong. The Mexicans made a brave and gallant defense, but were compelled to succumb. The battles of Contreras and Churubusco were fought on the same day, and were really one battle. In both actions the American loss was one hundred and thirty-nine killed and nine hundred and twenty-six wounded. The Mexican loss was near four thousand killed and wounded, with the loss of three hundred prisoners, thirty-seven cannon, and a large number of small arms with ammunition.

General Scott could easily have occupied the Mexican capital on the same day, but meanwhile Mr. Nicholas P. Trist had arrived from Washington with instructions from the President to endeavor to make a treaty of peace, and both he and General Scott thought it best to await the turn of events looking to that end. On the next morning, August 27, 1847, General Scott set out on the San Antonio road, and was met near Churubusco by a deputation bearing a white flag from the Mexican Government, proposing an armistice of thirty hours for burying the dead and collecting the wounded, which he at once rejected. The deputation accompanying the flag consisted of Señores Basadre, Mora y Villamil and Aranjos, who had been sent by Pacheco, Minister of Foreign Affairs. General Santa Anna expressed great dissatisfaction at the action of the Minister, on which he resigned. General Scott addressed a communication to the head of the Mexican Government and general in chief, in which he said that too much blood had already been spilled, and suggested that it was time the differences between the two republics should be settled. He mentioned (what was known to the Mexican authorities) that a commissioner on the part of the United States, clothed with full power to that end, was with his army. He expressed his willingness on reasonable terms to agree to a short armistice. While he proposed to wait until the next morning for a reply, he announced his intention "in the meantime to seize and occupy such positions outside of the capital as I may deem necessary to the shelter and comfort of this army."

The Mexican authorities, through Alcorta, Secretary of War and of the Navy, named two brigadier generals of the Mexican army, Mora y Villamil and Benito Quijano, to act as commissioners.

General Scott appointed as commissioners Major General John A. Quitman, Brigadier-General Franklin Pierce, and Brevet Brigadier-General Persifor F. Smith. The convention concluded its work on the 24th of August. It was agreed that hostilities should cease at once within thirty leagues of the Mexican capital. No work of a military character was to be done, and any re-enforcements or munitions of war except that now on its way to either army was to be stopped at a distance of twenty-eight leagues from the capital. The American army was not to obstruct the passage from the surrounding country into the capital of the ordinary supplies of food necessary for the subsistence of the Mexican army and the inhabitants within the city, nor were the Mexican authorities to obstruct the passage of supplies of subsistence from the city or country necessary for the supply of the American army. The armistice was to continue pending negotiations or until the commander of either army should give notice to the other of its cessation; and forty-eight hours after such notice General Worth, on the night of the 21st, moved his division to Tacubaya, where he was preceded by General Scott, and established his headquarters in the Bishop's Palace. General Quitman remained at San Augustin, to which point General Shields returned with his command. General Twiggs was at San Angel, and General Pillow at Mexcoac.

Previous to the occurrences just narrated, Major Folliot Thornton Lally had on August 6th marched with a force of about one thousand men from Vera Cruz. He was joined en route by a company of mounted Georgia volunteers, one of Louisiana mounted men, and two six-pounders, under command of Lieutenant Henry B. Sears, of the Second Artillery. General Don Juan Soto, Governor of the State of Vera Cruz, organized a force between one thousand and two thousand strong, a part of which were paroled prisoners, with the purpose of attacking Major Lally and capturing his wagon train, which was supposed to carry a large amount of silver coin. An attack was made by this force on Major Lally at the pass of Ovejas, the engagement lasting an hour and a half. Captains James Nelson Caldwell, of the Voltigeurs, and Arthur C. Cummings, Eleventh Infantry, were severely wounded. Nine enlisted men were wounded, one mortally. The Mexican loss is not known. On August 12th the command reached Puente Nacional and found the Mexicans in considerable force, strongly barricaded. An artillery fire was opened on them and they were driven back. The American loss in this affair was sixty killed and wounded. On approaching the battlefield of Cerro Gordo they were again attacked, and sustained a loss of one killed and eight wounded. Several other attacks of a similar character were made, but without success. Major Lally, with his troops and wagon train, arrived at Jalapa thirteen days out from Vera Cruz, when without interruption five days would have been sufficient for the march. Mr. Trist notified the Mexican Minister of Foreign Affairs, August 25th, of the object of his mission, and requested a meeting. He was advised that commissioners would meet him on the 27th at Azapotzalco, which was between the two armies. General Santa Anna, after appointing several persons who declined, named General Herrera, Señor Conto, General Mora y Villamil, Señor Atristain, and Secretary Miguel Arroyo. On the morning of the 27th, before the meeting of the commissioners, a train of wagons sent into the city to obtain supplies for the American army was met by a mob, stoned and driven away. Subsequently an apology was offered for this gross infraction of the armistice, and the wagons returned and secured their stores.