The Battle of Cer, also popularly known as Battle of the Jadar River, was fought in August 1914 between Serbia and Austria-Hungary during the early stages of the First World War.
http://totallyhistory.com/the-battle-of-cer/ The first aerial dogfight occurred during the Battle of Cer (15–24 August 1914), when Serbian aviator Miodrag Tomić encountered an Austro-Hungarian plane while performing a reconnaissance mission over Austro-Hungarian positions. The Austro-Hungarian pilot initially waved, and Tomić reciprocated. The Austro-Hungarian pilot then fired at Tomić with his revolver. Tomić managed to escape, and within several weeks, all Serbian and Austro-Hungarian planes were fitted with machine-guns.
https://en.wikipedia.org/wiki/Dogfight https://youtu.be/7aiuAYqwNKA