On the first day of the war, 18 October 1912, Delov's detachment advanced south across the border in four columns. The next day, they defeated the Ottoman troops at the villages of Kovancılar (present day: Pchelarovo) and Göklemezler (present day: Stremtsi) and then headed for Kardzhali. The detachment of Yaver Pasha left the town in disorder. With its advance towards Gumuljina, the Haskovo detachment threatened communications between the Ottoman armies in Thrace and Macedonia. For this reason, the Ottomans ordered Yaver Pasha to counter-attack before the Bulgarians could reach Kardzhali but did not send him reinforcements.^[17] To follow this order he had in command 9 tabors and 8 guns.^[16]

However, the Bulgarians were not aware of the strength of the enemy and on 19 October the Bulgarian High Command (the Headquarters of the Active Army under General Ivan Fichev) ordered General Ivanov to stop the advance of the Haskovo Detachment because it was considered risky. The commander of the 2nd Army, however, did not withdraw his orders and gave Delov freedom of action.^[15] The detachment continued with the advance on 20 October. The march was slowed by the torrential rains and the slow movement of the artillery but the Bulgarians reached the heights to the north of Kardzhali before the Ottomans could reorganize.^[18]

In the early morning of 21 October Yaver Pasha engaged the Bulgarians in the outskirts of the town. Due to their superior artillery and attacks on bayonet the soldiers of the Haskovo Detachment overran the Ottoman defenses and prevented their attempts to outflank them from the west. The Ottomans were in turn vulnerable to outflanking from the same direction and had to retreat for a second time to the south of the Arda River, leaving behind large quantities of munitions and equipment. At 16:00 the Bulgarians entered Kardzhali.^[19]

The Battle of Kircaali took place on 21 October 1912, when the Bulgarian Haskovo Detachment defeated the Ottoman Kırcaali Detachment of Yaver Pasha and permanently joined Kardzhali and the Eastern Rhodopes to Bulgaria. The defeated Ottomans retreated to Mestanlı while the Haskovo Detachment prepared defenses along the Arda. Thus the flank and the rear of the Bulgarian armies advancing towards Adrianople and Constantinople were secured.