At the end of June 1943, Allied forces assaulted New Georgia before the Japanese could complete construction of their defensive positions. Sasaki nonetheless was able to block the initial U.S. attempt to take Munda Airfield on 7 July. Despite reinforcements and a strong effort, Sasaki was forced to give up Munda on 4 August. Sasaki had no choice but to withdraw to Kolombangara. Under continued attack, the outlying islands were occupied one by one, and Kolombangara was isolated. Short of ammunition and provisions, Sasaki supervised the successful evacuation of some 9,400 Japanese defenders to Bougainville.
Reassigned to Eighth Army Area headquarters in November 1943, Sasaki was promoted to lieutenant general. He died at Tokyo on 27 April 1961.
Altobello, Brian J. Into the Shadows Follow: The Brutal Battle for New Georgia. Novato, CA: Presidio Press, 2000.; Morison, Samuel Eliot. United States Naval Operations in World War II. Vol. 6, Breaking the Bismarcks Barrier, 22 July 1942–1 May 1944. Boston: Little, Brown, 1950.