The German Ninth Army's right wing was XXV Reserve Corps, commanded by Lieutenant General Freiherr Reinhard von Sheffer-Boyadel, a 63-year-old who had been recalled from retirement. With Lieutenant General Manfred von Richthofen's, great uncle of the flying ace, cavalry in the van, they were pushing southeast between Łódź and the Vistula. Part of Rennenkampf's First Army was finally moving east to attack the Germans. Their re-positioning was hindered when a makeshift bridge across the river collapsed, so they had to cross by ferry or on the nearest usable crossing 85 km (53 mi) upstream. Once over they attacked the weakly defended side of the corridor extending south from the German frontier to their advancing spearhead. The Russians reoccupied Brzeziny, cutting the roads used by German XXV reserve corps, whose progress south was now blocked by the Russian Fifth Army. Sheffer was ordered to stop advancing, but the order did not reach him. Suddenly it was the Germans who were ensnared in a pocket. Mackensen stopped attacking toward Łódź, turning to help to extricate them. The ecstatic Russians ordered trains for up to 20,000 prisoners, actually the German fighting strength in the pocket was about 11,000, but there were also 3,000 wounded. Other sources state that 50,000 prisoners were anticipated.
Hindenburg was alarmed by the intercepted wireless messages ordering the trains, but Mackensen assured him that they would prevail. In the pocket, Richthofen's cavalry, which had been leading the advance, reversed direction to screen the rear of three infantry columns Sheffer formed along the roads for the retreat back northwest. The frozen, hungry Germans pushed on through the icy night. They reached the outskirts of Breziny unobserved, because most of the 6th Siberian Division were huddling in their sleeping quarters, trying to keep from freezing. The Germans attacked at dawn with bayonets on unloaded rifles and occupied much of the town before a shot was fired. The commander of 6th Siberian Division broke down. Swamped with conflicting accounts of German movements, and with the weather too foggy and the days too short for aerial observation, Ruzsky issued a series of orders, each contradicting the one before. He focused on preventing further German moves south instead of their thrust to the north. On 26 November, XXV Reserve Corps broke out of the pocket, bringing with them 12,000 prisoners, some taken during the breakout, who pulled 64 captured guns. Inconclusive fighting continued until 29 November when at a conference with his front commanders Grand Duke Nicholas ordered his forces in Poland to withdraw to defensible lines nearer to Warsaw. Hindenburg learned from an intercepted wireless that Łódź was to be evacuated.