On August 16, the Polish Assault Group commanded by Piłsudski began its march north from the Wieprz River. It faced the Mazyr Group, a Soviet corps that had defeated the Poles during the Kiev operation several months earlier. However, during its pursuit of the retreating Polish armies, the Mazyr Group had lost most of its troops and had been reduced to only one or two divisions covering a 150-kilometre front line on the left flank of the Soviet 16th Army. On the first day of the counteroffensive, only one of the five Polish divisions reported any sort of opposition, while the remaining four, supported by a cavalry brigade, managed to advance north 45 kilometres unopposed. When evening fell, the town of Włodawa had been liberated, and the communication and supply lines of the Soviet 16th Army had been cut. Even Piłsudski was surprised by the extent of these early successes. The Assault Group units covered about 70 kilometres in 36 hours. As planned, it split the Soviet fronts, disrupting the offensive, all without encountering any significant resistance. The Mazyr Group had already been defeated on the first day of the Polish counterattack. Consequently, the Polish armies found what they had hoped for—a large opening between the Soviet fronts. They exploited it ruthlessly, continuing their northward offensive with two armies following and falling on the surprised and confused enemy.