After returning to his home village, Zykov joined the Red Army at Kotelnich in May 1918 during the Russian Civil War and was sent to the 82nd Rifle Regiment of the 10th Rifle Division. As an assistant company commander and company commander, he fought with the regiment on the Northern and Northwestern Fronts in the Pskov and Gdov districts. He was shell-shocked in February 1919, wounded in the arm in June near the village of Tuloksa, and wounded in the foot near Dno in October. After the regiment was transferred to the 18th Rifle Division in November 1919, Zykov served as a battalion commander, assistant regimental commander, and deputy regimental commander in fighting against British and Finnish troops in the Olonets district. For distinguishing himself during 1919, Zykov subsequently received the Order of the Red Banner twice, in 1919 and 1924.