In the Disaster of Rancagua (1814) he was able to defeat the forces of Bernardo O'Higgins and Jose Miguel Carrera.

With Osorio's victory at Rancagua, the period known as "reconquest" (Reconquista) of Chile had begun.

Osorio sought to reinstate order and justice and with military measures he prevented the onslaught of the insurgents.

[2] In 1816 he returned to Lima and Francisco Marcó del Pont was made new Governor of Chile.

The Battle of Maipu, however, was a major defeat for the Spaniards, and it signified the end of the Spanish authority in almost all of Chile, with the exception of the island of Chiloé and the city of Valdivia.