 In 1936, Sakai was appointed commander of the IJA 24th Infantry Brigade, and was assigned to China with tensions rising in the prelude to the Second Sino-Japanese War.From 1937-1938, he was commander of the IJA 1st Independent Mixed Brigade, which participated in Operation Chahar to seize Chahar Province from China.After the success of that operation, Sakai was transferred to rear echelon operations as commander of the IJA 7th Depot Division in 1938 and the IJA 109th Division in 1939.