By 1759, Prussia had reached a strategic defensive position in the war. Upon leaving winter quarters in April 1759, Frederick assembled his army in Lower Silesia; this forced the main Habsburg army to remain in its winter staging position in Bohemia. The Russians, however, shifted their forces into western Poland and marched westward toward the Oder river, a move that threatened the Prussian heartland, Brandenburg, and potentially Berlin itself. Frederick countered by sending an army corps commanded by Friedrich August von Finck to contain the Russians; he sent a second column commanded by Christoph II von Dohna to support Finck.

General Carl Heinrich von Wedel, the commander of the Prussian army of 26,000 men, attacked a larger Russian army of 41,000 men commanded by Count Pyotr Saltykov. The Prussians lost 6,800–8,300 men; the Russians lost 4,804.

The loss at Kay laid open the road to the Oder river and by 28 July Saltykov's troops had reached Crossen. He did not enter Prussia at this point, though, largely due to his problematic relationship with the Austrians. Neither Saltykov or Daun trusted one another; Saltykov neither spoke German nor trusted the translator. On 3 August, the Russians occupied Frankfurt, while the main army camped outside the city on the east bank, and began constructing field fortifications, in preparation for Frederick's eventual arrival. By the following week, Daun's reinforcements joined forces with Saltykov at Kunersdorf.