[2] He later left for the Viceroyalty of Peru in the Spanish Empire and arrived in Buenos Aires in 1701, where he was conferred the position of sargento mayor.
García Ros was a brave soldier who fought successful campaigns against the Aboriginal Charrua, Yaro, and Bohanes during this time.
[2] In 1705, with Juan de Lacoizqueta, García Ros participated in the Siege of Colonia del Sacramento to take the town from the Portuguese, as part of the War of the Spanish Succession.
After Manuel de Robles Lorenzana arrived to lead Paraguay, he returned to Buenos Aires where he served in the government there.
Ros's force, composed largely of mission Indians, was soundly defeated by a surprise attack from Antequera's Paraguayan militia.