German I Corps commander Hermann von Francois not only had deployed all of his infantry in the front line: by staying out of his headquarters to avoid unwanted interference from his superiors, he also lost track of half of his forces. Fortunately for the Germans, Maj. Gen. Adalbert von Falk of 2nd Infantry Division (just starting his second week on the job) heard the crash of fighting around Gumbinnen and gathered one of his brigades to march to the sound of the guns

Falk's attack took the Russians by surprise, finding their open left flank and proceeding to roll them up. Conta's 1st Division went over to the attack when they saw the Russians falter, and the 27th Infantry Division fell back in near-total panic. The Russian division's losses topped 3,000 prisoners and another 3,000 dead and wounded.