On July 7, 1520, at the Battle of Otumba, Mexico, Hernán Cortés and the Tlaxcalans defeated a numerically superior Aztec army. An excerpt from the article:
"The Spanish invaders who managed to escape from Tenochtitlan were weak, dispirited and wounded. The new Emperor of the Mexica, Cuitláhuac, decided that he had to try and crush them once and for all. He sent a large army of every warrior he could find under the command of the new cihuacoatl (a sort of captain-general), his brother Matlatzincatzin. On or about July 7, 1520, the two armies met in the flatlands of the Valley of Otumba.
The Spanish had very little gunpowder left and had lost their cannons on the Night of Sorrows, so the harquebusiers and artillerymen would not factor into this battle, but Cortes hoped he had enough cavalry left to carry the day. Before the battle, Cortes gave his men a pep talk and ordered the cavalry to do their best to disrupt the enemy formations.
The two armies met on the field and at first, it seemed as if the massive Aztec army would overwhelm the Spanish. Although Spanish swords and armor were far superior to native weapons and the surviving conquistadors were all battle-trained veterans, there were far too many enemies. The cavalry did their job, preventing the Aztec warriors from forming up, but there were too few to win the battle outright.
Spotting the brightly dressed Matlatzincatzin and his generals at the other end of the battlefield, Cortes decided on a risky move. Summoning his best remaining horsemen (Cristobal de Olid, Pablo de Sandoval, Pedro de Alvarado, Alonso de Avila and Juan De Salamanca), Cortes rode at the enemy captains. The sudden, furious assault took Matlatzincatzin and the others by surprise. The Mexica captain lost his footing and Salamanca killed him with his lance, capturing the enemy standard in the process.
Demoralized and without the standard (which was used to direct troop movements), the Aztec army scattered. Cortes and the Spanish had pulled out a most unlikely victory."