Under the command of Lieutenant General Kliment Boyadzhiev, the Bulgarians seized the fortified areas of Pirot, Niš and the valley of the river Morava.

Due to the harsh weather, the defenders' strong resistance and the rough terrain, early Bulgarian advance was slow.

But because the defenders were severely outnumbered, the Bulgarians broke through near Pirot in 10 days, and the Serbs retreated to the Timok.

The battle continued for 27 days, and the Bulgarians penetrated up to 90 km deep into Serbia's territory.

The Serbs lost 6,000 men, 60 guns, and a large amount of military equipment.