The Spanish knew what was coming. After the failed Dutch expedition of 1641, the garrison at San Salvador had sent urgent appeals to Manila for reinforcements. Governor-General Sebastian Hurtado de Corcuera, already stretched thin across the sprawling Spanish East Indies, responded with two small vessels carrying twelve sailors and twenty soldiers. The reinforcement was an insult wrapped in logistics - barely enough men to replace normal attrition, let alone defend against a determined assault. Morale inside the fort collapsed. The previous year's battle had already cost Spain its indigenous allies in the Danshui region. Aboriginal communities that had once cooperated with Spanish missionaries and traders now aligned with the Dutch, who had demonstrated superior force. The garrison was isolated, under-supplied, and defending a position that Manila had all but written off. When the Dutch fleet appeared on the horizon, the Spanish prepared for a siege they had little realistic hope of surviving.

The Dutch plan was straightforward: land forces on San Salvador island, capture the hilltop positions overlooking the main fortress, and use those positions to force surrender. The Spanish knew this and counterattacked the landing party with everything available - twelve Spanish soldiers, eight Pampangan fighters from the Philippines, and thirty to forty aboriginal archers still loyal to the garrison. The defense was fierce. Spanish muskets fired into the packed landing boats, sometimes loaded with three balls per shot. The indigenous bowmen, described by Spanish accounts as very skillful, inflicted heavy casualties on the Dutch as they waded ashore. But numbers and equipment decided the outcome. The Dutch maintained discipline under fire, forced the defenders to retreat, and climbed the hill to capture the Mira, a forward position. They then turned their guns on La Retirada, the redoubt protecting the main approach. The Spanish defenders were few and exhausted, but they fought with the desperation of men who understood the stakes. One Spaniard later wrote that for every ten balls they fired, the Dutch responded with two hundred or more. Another described the bombardment as so incessant that it seemed like Judgment Day. After four days of continuous fire, the Dutch battered the walls down and stormed the position.

With the redoubt captured, the Dutch positioned their cannon above the main fortress and sent a messenger under a white flag carrying a letter written in Latin - the diplomatic language both colonial powers understood. The letter demanded surrender. The Spanish governor accepted. The formality of the exchange, conducted in a dead language on a remote Pacific island between two empires competing for trade routes half a world from home, captures something essential about seventeenth-century colonialism: even its violence was wrapped in protocol. After the surrender, the Dutch confiscated Spanish arms and flags. The defeated garrison was shipped first to Tayouan in southern Formosa, then to Batavia in the Dutch East Indies, and finally back to Manila. The Dutch had achieved complete control of Formosa. The Spanish colonial presence on the island, which had begun in 1626, was finished.

The fall of Formosa needed a scapegoat, and Manila found one in Governor-General Corcuera. In 1644, his successor Diego Fajardo Chacon had Corcuera arrested and imprisoned to stand trial for the loss of the island. The prosecution's charges were specific and damning: Corcuera had ordered the destruction of Fort Santo Domingo, dismantled the redoubt protecting San Salvador, withdrawn three of the four companies defending the colony, and installed as its final governor a soldier so unsuited to command that he could neither read nor write. These decisions, the prosecution argued, were the total cause of the loss of the Isla Hermosa - the Beautiful Island, as the Portuguese had named Formosa. Corcuera spent five years imprisoned in the Philippines while the trial dragged through colonial bureaucracy. A contemporary observer noted the irony with undisguised fascination: Don Sebastian had been the most absolute and the most dreaded lord in the world, and now he sat in a Manila cell. A royal pardon eventually freed him. He was offered the governorship of Panama in 1651 but declined. In 1659, he accepted the post of governor and captain-general of the Canary Islands, where he served until his death the following year - a long fall from the man who once commanded Spain's Pacific empire.