Independence forces win the Battle of Maipú, Chile on April 5, 1818. 

Bicentenary Battle of Maipú
Correos Chile issued this stamp April 5, 2018
Designer: Mauricio Navarro González

The independence forces (Army of the Andes and the Chilean Army) met Spanish Royalist and loyalist forces on the Maipú plains, near Santiago, Chile.  

James Houser over at The Unknown Soldiers Podcast wrote an excellent description of the fight and did a far better job than I could in describing the battle and participants:

April 5, 1818. In the shadows of the Andes, a confrontation is about to take place. The ragtag Army of the Andes, led by Jose de San Martin, prepares to confront the Spanish army that stands between them and the independence of South America. On the plains of Maipu, near Santiago, Chile, the fate of the Spanish Empire is about to be decided. April 5, 1818 – Latin American Wars of Independence & Battle of Maipu (unknownsoldierspodcast.com)

Head over and read his entire description. He also supplies a recommended reading list! He’s an excellent story teller. Highly recommened.