 The Serbs beat back an Austro-Hungarian invasion in August, at the Battle of Cer. It marked the first Allied victory over the Central Powers in World War I. Potiorek was humiliated by the defeat and was determined to resume the assault against the Serbs. He was given permission in September to launch another invasion of Serbia provided that he "[did not] risk anything that might lead to a further fiasco." Under pressure from the Russians to launch their own offensive and keep as many Austro-Hungarian troops as possible away from the Eastern Front, the Serbs invaded Bosnia in September with the help of Chetnik irregulars but were repulsed after a month of fighting in what came to be known as the Battle of the Drina. Bojović was wounded during the battle and was replaced by Živojin Mišić as commander of the Serbian 1st Army.
