On September 20, 1905, the armed corps of the Cretan chieftain Efthymios Kaoudis (1866-1956) set out from the Monastery of the Holy Trinity of Pisoderiou with the aim of ambushing the Bulgarian Komitadjis between the villages of Ostima (now Trigono of Florina) and Tirnovo (now Prasinada of Florina). Since mid-September, there was information that a considerable number of IMRO (Internal Macedonian Revolutionary Organization) men had gathered in this area.

Upon reaching Ostima, Kaoudis' forces set up an ambush on the eastern side, anticipating an attack by the Bulgarian Komitadjis. The first clash occurred at the entrance to the village on the morning of September 21, resulting in the injury or death of three or four Komitadjis.

Recognizing the enemy's numerical advantage, Kaoudis ordered his men to climb the hill near the village. The experienced Cretans, Nistaris and Kalogerakis, successfully took the hill, killing one Komitadji and forcing three others to retreat. This gave the forces of Efthymios Kaoudis a strategic advantage in the conflict, which continued until an Ottoman military detachment intervened to end it.

The Battle of Ostima proved decisive for the progression of the Macedonian Struggle. It marked the first organized attack by Greek Macedonian fighters after the death of Captain Vangelis Strembeniotis and the capture of Captain Kottas Christou. Despite the significant numerical disparity (87 Exarchists versus 20 Greek Macedonian fighters), the battle highlighted the military capability and combat experience of the Greek Macedonian fighters and had a positive effect on the morale of the Greek fighters and the Greek Orthodox residents in the surrounding areas.

In addition to the morale boost, the Komitadjis suffered significant military losses in the Battle of Ostima. Beyond the morale boost, the Komitadjis suffered significant military losses in the Battle of Ostima. According to Efthymios Kaoudis, 5 Comitadji were killed during the battle and at least another 15 were wounded. The Greek Macedonian fighters had only two wounded, one of whom, Emmanouil Skoundris, sustained severe injuries.

Significant assistance to Kaoudis's forces was provided by the villagers of Zelovo (now Antartiko, Florina) and Pisoderi. The presence of the Macedonian fighter and priest at Pisoderi, Father Stavros Tsamis (1870-1906), was also crucial. Father Stavros, on the one hand, alerted the Ottoman authorities about the conflict, while on the other, he provided care in his home for the severely wounded Emmanouil Skoundris. Simultaneously, by sending his brother, Lazaros Tsamis, to Albania, he secured military supplies for the arming of Efthymios Kaoudis's armed group