Following the successful capture of Nalbankioi (now Perdikkas) on October 16, the commander of the V Division, Colonel Dimitrios Mattheopoulos, issued an order for the Greek forces to advance to the northwestern territories of Western Macedonia. In accordance with the strategic plan, the advance guard of the V Division advanced as far as the village of Zaberdani (now Lofoi) on October 19.

In light of the occupation of Giannitsa by the majority of the Army of Thessaly's military forces on October 20, Colonel Mattheopoulos opted to advance the V Division to Monastiri (now Bitola). Based on intelligence obtained from Bulgarian Komitadjis, the Major concluded that the Ottoman forces in the area were scarce and exhibited a lack of morale and willingness to resist.

The operation to occupy Monastiri commenced at 10:30 a.m. on October 21, but was delayed due to coordination issues concerning the formation of the right wing. However, the Division was soon compelled to address more pressing concerns, as it became evident that the initial intelligence regarding the strength of Ottoman forces was inaccurate. At the outset of the operation, the vanguard of the right column, advancing from the village of Zaberdani towards Vostereni (now Meliti) was confronted with the presence of formidable Ottoman forces belonging to the XVIII Ottoman Division, which had assembled in the area following the Serbs' occupation of Skopje.

Under the constraints of time, the Division was compelled to transform its initial offensive plan into a defensive one. This new strategy entailed the deployment of a battalion to Ano Kalenik (now Ano Kalliniki) and another to Florina. The objective was to encircle the enemy and impede any potential Ottoman attempt at escape. However, the numerical superiority of the Ottoman army rendered the implementation of the defensive plan unfeasible. As a result, the regiments of the V Division commenced a retreat towards Banitsa (now Vevi), with the Ottomans pursuing them with relentless determination. Despite the Greek forces' best efforts to maintain control of Banitsa, they were ultimately unable to prevent the Ottoman army's advance. As a result, the Greek forces continued their retreat in a disorderly manner towards the Kirli-Derven Pass (Klidi Pass), where they were concentrated at night in Sorovits (now Amyntaio) and a little further south, in the village of Sotiras.

The battles that occurred along the line of Zaberdani – Banitsa – Kirli Derven Pass on October 21, 1912, signified the initial retreat of the Greek army since the inception of the First Balkan War. During the course of the battle, the Greek forces sustained considerable losses, with two officers and 166 privates killed, four officers and 192 privates wounded, and ten soldiers captured. The following day, the V Division initiated the process of regrouping and organizing a counterattack.