Spanish governor Don Manuel de Montiano commanded the invasion force, which by some estimates totaled between 4500 and 5000 men. Of that number, roughly 1900 to 2000 were ground assault troops. Oglethorpe's forces, consisting of regulars, militia, and native Indians numbered less than 1000. The garrison at Fort St. Simons resisted the invasion with cannonade, but was not able to prevent the landing. On July 5, 1742 Montiano landed nearly 1900 men from 36 ships near Gascoigne Bluff, close to the Frederica River. Faced with a superior force, Oglethorpe decided to withdraw from Fort St. Simons before the Spanish could mount an assault. He ordered the small garrison to spike the guns and slight the fort (doing what damage they could), to deny the Spanish full use of the military asset. The Spanish took over the remains of the fort the following day, establishing it as their base on the island.
After landing troops and supplies, and consolidating their position at Fort St. Simons, the Spanish began to cautiously reconnoiter beyond their perimeter. They found the road between Fort St. Simons and Fort Frederica, but first assumed the narrow track was just a farm road. On July 18, the Spanish undertook a reconnaissance in force along the road with approximately 115 men under the command of Captain Sebastian Sanchez.
A mile and a half short of Fort Frederica, their target, the Spaniards were set upon by a force consisting of Georgia Rangers, and the Highland Independent Company, aided by more numerous Chicksaw, Yamacraw and Creekwarriors, all under General Oglethorpe's personal direction. After an intense but brief battle, lasting less than one hour, Oglethorpe's forces succeeded in killing or capturing 36 of the Spaniards, nearly a third of the forces in that group. Among those killed was second-in-command, Captain Nicolas Hernandez. Captain Sebastian Sanchez was captured. Oglethorpe's losses were described as "light".
The rest of the Spanish retreated in disorder back to the south. They were met by 200 Spanish grenadiers under Captain Antonio Barba, who had just marched from Fort St Simons and covered their retreat.