The Niš Operation

Initially, bad weather and impassable terrain delayed the Bulgarian advance. Despite desperate Serbian resistance, the defence collapsed after the Knjaževac Detachment withdrew on 12–13 October under pressure from the 8th Tundzha Infantry Division. This forced Serbian units to abandon the Pirot fortified position on 14 October as well. The First Army continued its pursuit, advancing towards Niš after the breakthrough. Following fierce fighting, the Bulgarian army reached the outskirts of Niš on 22 October. Units of the First Army's northern and eastern groups began assaulting the city simultaneously. At 4 p.m. Bulgarian time, the 4th Pleven Infantry Regiment of the 9th Pleven Division broke through Niš Fortress's defensive line in a frontal bayonet attack. The Serbs fled in panic, leaving the entire fortified line in Bulgarian hands. On the morning of 23 October, the Bulgarian army entered the abandoned fortress without a fight, triumphantly capturing enormous quantities of supplies, ammunition and new weapons. Thousands of soldiers who had deserted the Serbian army surrendered, while the remaining Serbian units withdrew in disgrace across the Morava towards Kosovo Polje, making a final attempt to fight a decisive battle and salvage Serbian military honour. Niš's fall had an enormous psychological impact on Bulgarian national and military morale. The Serbian royal court and Nikola Pašić's government had resided there since the war began and were forced to abandon their wartime capital, fleeing towards Kosovo. From 24 October, the Bulgarian army continued driving the remaining Serbian units towards Kosovo Polje.

The battle ended in a tactical victory for the Bulgarian forces.