On May 4, 1906, the armed corps of the Greek Macedonian fighters received an order from the center of Monastir (now Bitola) to attack the village of Osnitsani (now Kastanofyto), where about a hundred Komitadjis of Mitros Vlachos and Kyriazos were camped. The leader of the operation was Antonis Vlachakis (Captain Litsas) who, upon reaching the Monastery of St. Athanasius of Zikovitsa, divided his armed body of about 85 men into six groups led by Vangelis Vlachos, Evangelos Bairaktaris (Captain Akyllas), Ioannis Christopoulos (Captain Vourkanos), Panagiotis Petropoulakis and Loukas Kokkinos. The sixth group was commanded by him with Leonidas Petropoulakis as second in command. According to the plan, Vlachakis' corps would attack Osnitsani while the other five would support the attack.

On May 7, 1906, the Greek Macedonian fighters advanced to Osnitsani with the aim of attacking the Exarchist band of Mitros Vlachos and the house of Voevoda Doukas. However, Captain Litsa's group met stiff resistance from the organized Komitadjis, as well as from the 750 Ottoman hunters (members of the Abji Tabour battalions) who participated in the battle. Captain Litsas ordered the burning of four houses and tried to plant explosives in the house of a Bulgarian Exarchist, Tsiurka. However, the device exploded, killing the Greek leader and his deputy, Leonidas Petropoulakis.

Despite the loss of Captain Litsas, the six groups of Greek Macedonian fighters continued to fight against the opposing forces, which were now reinforced by Ottoman soldiers who had arrived in the area. Under these circumstances, the retreat of the Macedonian fighters was necessary, difficult and resulted in significant losses. Seven soldiers of Loukas Kokkinos lost their lives, while another seven were killed while trying to return to Osnitsani to collect the body of the seriously wounded Leonidas Petropoulakis.

Overall, the losses in the battle of Osnitsani were heavy for both sides. There were many wounded and 24 Greek Macedonian fighters, 9 Komitadjis and about 144 Ottoman officers and soldiers lost their lives. The battle lasted about eight hours and is one of the most important events of the Macedonian struggle. The Greek State, in honor of the Macedonian fighters who lost their lives in the Battle of Osnitsani, issued a Presidential Decree (No. 759/29.10.1960, Official Gazette 183, Vol. A, 19.11.1960) providing for an annual commemoration ceremony ceremony in Damaskinia.