Weix felt that something was wrong and ordered him to join the reserves. On 18 December, the German 27th Panzer Division and the 385th Division marched to the west side of the Soviet breakthrough, and a battle group was divided into a battle group and the German 298th Division assembled on the east side of the breakthrough. Weix also drew the 387th Infantry Division from the German 2nd Army (Voronezh area) and reached Kandemirovka (southwest of the breakthrough) on 18 December. However, the powerful impact of the four Soviet tank armies could not be stopped by a single German armored division and several infantry divisions. The German 27th Panzer Division was soon defeated. The hastily established support points by the Germans were also easily bypassed by the Soviets.
On 18 December, the Guards 1st Army and the 6th Army expanded the breakthrough to a width of 60 km and a depth of 40 km. Tank armies blocked a large number of German-Italian troops south of Boguqar. The Italian 3rd, 9th, and 52nd Divisions, the German 298th Division, and the Italian "March 23" and "January 3" Blackshirt Brigades were gradually surrounded.
The central defensive zone of the Italian 8th Army was completely destroyed, and the entire army group collapsed. A large number of officers and men desperately fled south for their lives. Italian Major Troy later recalled: "Many of the commands began to move from their locations, losing all contact with the troops. Troops attacked by tanks scrambled to flee for their lives", "artillery and cars were abandoned. Many officers tore off rank identification and soldiers threw away their machine guns, rifles and equipment."
On the eastern front, the 3rd Guards Army also continued to attack the German 294th Division, and also put in the 1st Guards Mechanized Army (163 tanks), which occupied Bokovskaya on December 18, penetrating the German line for about 15 kilometers. The German 22nd Panzer Division attempted to contain the Soviet advance. But this is clearly unsustainable.