In the early 1270s, Michael VIII Palaiologos launched a major campaign against John I Doukas, ruler of Thessaly. It was to be headed by his own brother, the despotes John Palaiologos. To prevent any aid coming to him from the Latin principalities, he also dispatched a fleet of 73 ships, led by Philanthropenos, to harass their coasts. The Byzantine army, however, was defeated at the Battle of Neopatras with the aid of troops from the Duchy of Athens. At the news of this, the Latin lords took heart, and resolved to attack the Byzantine navy, anchored at the port of Demetrias.

The Latin fleet caught the Byzantines by surprise, and their initial attack was so violent that they made good progress. Their ships, on which high wooden towers had been erected, had the advantage, and many Byzantine seamen and soldiers were killed or drowned. Just as victory seemed within the Latins' grasp, however, reinforcements arrived led by the despotes John Palaiologos. While retreating from Neopatras, the despotes had learned of the impending battle. Gathering whatever men he could, he rowed forty miles in one night and reached Demetrias just as the Byzantine fleet was beginning to waver.

His arrival boosted the Byzantines' morale, and Palaiologos's men, ferried on board the ships by small boats, began to replenish their casualties and turn the tide. The battle continued all day, but by nightfall, all but two Latin ships had been captured. The Latin casualties were heavy, and included the triarch of Negroponte Guglielmo II da Verona. Many other nobles were captured, including the Venetian Fillippo Sanudo, who was probably the fleet's overall commander. The victory at Demetrias went a long way to mitigating the disaster of Neopatras for the Byzantines. It also marked the beginning of a sustained offensive across the Aegean