On July 2, 1907, Sergeant Major Georgios Tombras (Captain Roupakias) and Sergeant Nikolaos Platanias (Captain Lachtaras) met and decided to attack the village of Grentsi (now Ptelia of Kastoria), where, according to information, Voivode Atanas Kersakov was with his armed body. In the early hours of July 3, the Macedonians reached the village and entered without resistance. There they captured some of the inhabitants, including the teacher, the priest, the mukhtar and six other foremen.

When the Macedonians left the village, Kersakov's men, lurking on the surrounding hills, attacked by surprise. The Greek forces took up battle positions and counterattacked the Komitadjis' forces. At the same time, they executed the captured villagers who tried to escape. As the battle continued, a detachment of the Ottoman army arrived in the area. The Macedonians were temporarily caught between two fronts, but probably after Kersakov was mortally wounded, the Komitadjis retreated. According to contemporary reports, a battle with the Ottoman soldiers ensued, which lasted for about two hours and ended with the retreat of the Ottoman forces.

The armed groups of the two Greek chieftains achieved an important victory at Grentsi. In particular, the killing of the chief militant Kersakov was a heavy blow to the Internal Macedonian Revolutionary Organization (IMEO) and contributed to the predominance of Greek forces in the wider Korestia area.