The Battle of San Lorenzo was fought on February 3, 1813 in San Lorenzo, Argentina, then part of the United Provinces of the Río de la Plata. A Spanish Royalist force under the command of Antonio Zabala was defeated by the Regiment of Mounted Grenadiers, under the command of José de San Martín. This battle was the baptism of fire for this military unit, and for San Martín in the Spanish American wars of independence.