Here 's an interesting story about ahuehuetes Roger, the truth is that the conquest of Tenochtitlan by the spanish was not really performed by the spanish, it was performed by a combination of factors:
1.- The aztec superstition that Quetzalcoatl ( aztec god ) was going to return, Quetzalcoatl was described as a white man so when the Spanish conquistadors appeared aztecs thought that Cortez was Quetzalcoatl.
2.- The sighting of a comet which in aztec religion was seen as a sign of Quetzacoatl 's return
3.- Aztecs were pretty much hated by the tribes they conquered like the tlaxcaltecans, this tribes became allies to the Spanish conquistadors.
4.- Biological warfare, one of Cortez men had small pox, europeans were pretty much "inmune" to small pox, but the native americans were not, small pox, measles, chicken pox and other diseases were unknown by the native american inmune system. Inadvertedly the Spanish introduced this diseases decimating the native american population.
5.- The way in which aztecs waged war, aztecs took prisoners either for ransom or to be sacrificed to their gods, instead of killing the Spanish soldiers they took them prisoners.
At first when Cortez arrived he was mistaken as a god, then when the aztecs saw that he was no god they fought him defeating his army, during the retreat of Cortez ' army happend on of the most memorable days in Mexican history, it 's called "La Marcha de la Noche Triste" ( the march of the sad night ) where Cortez sawing his army defeated cried at the base of a tree, that tree was an ahuehuete; and to this day ( 485 years later ) the tree is still alive and it 's a national monument.
After the retreat Cortez formed an alliance with the tlaxcaltecans, with allies and reinforcements he returned to Tenochtitlan which by that time had already being decimated by small pox, it took no effort to Cortez to conquer Tenochtitlan because there was no one to defend it.
So the conquest of Tenochtitlan was not really peroformed by the military ability of Cortez nor the superiority of the Spanish expedition, it was performed by a combination of factors, the true conquerors of the Aztec Empire were the native tribes and the small pox.