On 21 November 1912, Greek naval forces under Rear Admiral Pavlos Kountouriotis landed at Mytilene. The admiral had already seized Lemnos and thrown a blockade across the Dardanelles, bottling up the Ottoman fleet and leaving the Aegean in Greek hands. At Mytilene he issued an ultimatum, and after negotiations the Ottoman garrison was given time to abandon the city. Kountouriotis then sailed off with the bulk of his ships, leaving only a cruiser squadron and two destroyers, and a militia of local Greeks he had hastily formed. The capture of the capital was the easy part. The Ottoman troops, some fifteen hundred to two thousand men, had not surrendered. They withdrew fifty kilometers northwest to a fortified camp at Filia, well stocked with provisions and munitions, and there they prepared to hold the island's interior.

What followed was a slow, difficult campaign across winter terrain. The small Greek force at Mytilene was not strong enough to finish the job, so general headquarters sent reinforcements and placed the operation under Colonel Apollodoros Syrmakezis, who assembled roughly 3,175 men and eight guns. He split them into two columns, a southern one at Lambou Myloi and a northern one at Thermi, and pushed them toward Filia. The advance was hard. The southern column was halted by stiff Ottoman resistance near the Leimonas Monastery, while the northern column moved faster, reaching the camp's outskirts by nightfall. The fighting was not without cost to the island's people. As they retreated, Ottoman forces carried out reprisals against the local Christian population, most notably at Petra, where they set the houses aflame. These were villagers caught in a war between armies, and the burning of Petra remains part of what the island remembers.

The end came in confusion. As both Greek columns prepared their final assault on Filia, an Ottoman envoy appeared asking for an armistice. It was granted, but when Major Abdul Ghani, the Ottoman commander, arrived, he denied having requested any negotiation and offered nothing. Reading this as a stall for time, Syrmakezis ordered the attack resumed at two in the afternoon. Then, at ten that night, the same envoy returned, this time carrying a letter of surrender signed by the garrison's officers. The instrument of surrender was formalized at eight the next morning, 21 December 1912. The whole campaign had cost the Greeks nine men killed and eighty-one wounded, a small toll for a strategic prize. Lesbos was, for the first time in nearly five centuries, no longer Ottoman.

Winning the island and keeping it were two different matters. The Ottoman Empire refused to concede the Aegean islands it had lost, and their fate passed to the Great Powers under the 1913 Treaty of London. In February 1914 the Powers ceded most of them, Lesbos included, to Greece, withholding only Imbros and Tenedos near the Dardanelles. Even then the question festered. A naval arms race followed, and by the summer of 1914 a fresh Greco-Turkish war looked imminent, averted only by the outbreak of the First World War. When a German cruiser entered Ottoman service that August, she was pointedly renamed Midilli, the old Turkish name for Lesbos, a token of claims not yet abandoned. Only the Treaty of Lausanne in 1923 settled the matter for good, and made the island's place in Greece final.