The battle of Puebla was almost a French loss from the get go. Badly managed and poorly coordinated it was a testament to how poorly the Mexicans were equipped that the French only suffered 400 dead. They walked into a killing field plain and simple.
The arrogance of the Europeans arriving in Mexico was palatable, for instance here is what Lorencez, the commander of the French forces at the battle, wrote just prior to it: "[the French] are so superior to the Mexican in terms of race, organization and moral discipline that now at the head of 6,000 soldiers I am the master of Mexico"
They felt no need to try and defeat the Mexicans with clever tactics.