Ocana is a rare battle where the Spanish fight the French in large numbers with no support. The Spanish have taken strategic initiative and are advancing on Madrid from North and South. The French don't notice the Southern approach at first and a mere 35 miles from Madrid there are some initial encounters that have the Spanish counter march and daddle. Soon the French have raced reinforcements to counter this thrust.
The day before the battle sees a huge cavalry action where the Spanish come off poorly. This is important as the right wing of the Spanish army is a VERY brittle cavalry formation facing enthused and strong French cavalry. The line of defensive was well chosen as on the right was a gullied river that blocked the Spanish from advancing on the Left wing.