When Operation Barbarossa began on 22 June 1941, Gusarov was stationed with the 12th Fighter Aviation Regiment. On 5 November, he was awarded the Order of the Red Banner. On 26 December, the regiment became the 486th Fighter Aviation Regiment. In 1942, he joined the Communist Party of the Soviet Union. During the summer of 1942, he fought in the Battle of Kharkov while flying an LaGG-3. Gusarov provided air cover for Soviet ground troops during the Battle of Kursk during summer 1943. On 5 July, he shot down a German fighter and rammed another while flying a Lavochkin La-5 over Ponyri. He was awarded his second Order of the Red Banner on 16 September. By November, Gusarov had reportedly made 432 sorties, and in 69 air battles shot down 15 German aircraft. He also claimed 14 shared victories. On 4 February 1944, Gusarov was awarded the title Hero of the Soviet Union and the Order of Lenin for his actions in air combat. In June 1944, the regiment was moved to the 5th Air Army to fight in the Second Jassy–Kishinev Offensive. Gusarov, Captain Andrei Girich and Senior Lieutenant Telegin together shot down two Focke-Wulf Fw 189 reconnaissance aircraft during the offensive. In January 1945, Gusarov participated in the Budapest Offensive, shooting down one Junkers Ju 52. He received the Order of Alexander Nevsky on 18 January. During the Prague Offensive in early May, he shot down at least one German aircraft. Gusarov was awarded the Order of the Patriotic War 1st class on 11 June.