Beauchef and his small army arrived at Trumao where they were aided by local Mapuche-Huilliche who ferried them over Bueno River and provided the Spanish with ox carts.

On March 6, Colonel Beauchef sent an advanced scouting group of 50 soldiers under the command of captain José María Labé.

Labé managed to maintain his ground for about an hour answering the fire, but finally started to retreat overwhelmed by the numerically superior enemy.

When Beauchef heard the shots, he decided to intervene with the 90 soldiers under his command, while allowing Labe's troop to move to his rear, in order for them to rest and recharge his ammunition.

Beauchef immediately seized the opportunity and ordered a frontal bayonet counter-charge with all the forces under his command, causing the Royalists to flee.