In September 1847, the Americans received incorrect information that a foundry was casting cannons for the Mexican Army at Molino del Rey, a complex of stone buildings used by Santa Anna to defend Mexico City. General Scott ordered an assault on September 8. The Mexican Army repulsed repeated assaults before finally falling to U.S. forces.

Scott then focused on the fortified hilltop of Chapultepec, Mexico's military academy at that time outside Mexico City. Artillery pummeled the fortress on September 12, before Scott sent his troops with ladders to scale its walls. After brutal fighting, the Americans rushed inside to meet Mexican defenders, including young cadets like the Niños Héroes. Scott's forces regrouped and turned toward the city.

Wanting to avoid the house-to-house fighting that occurred in Monterrey, Mexico City officials met with Santa Anna, who agreed to withdraw. On September 14, Scott’s army marched into the Central Plaza. Borland, a prisoner at the National Palace for months, said: “The whole of our little army ... took up quarters in the far-famed Halls of the Montezumas. You must imagine my feelings (a contrast to my first entree) when I rode through the streets that morning! I will attempt no description.”