As the Reds were losing the war, Antikainen fled to the Soviet Russia in late April 1918. He was one of the founders of the exile Communist Party of Finland, established in Moscow in August 1918. Antikainen took a course in the Petrograd Red Officer School and graduated in the spring of 1919. In the Russian Civil War, he fought against the Finnish Whites in East Karelia. In January 1922, Antikainen commanded a battalion in the Battle of Kimasozero, where a Red Army unit composed of Finnish Reds beat the Whites and pushed them back to Finland. The 1937 film "Za Sovetskuyu Rodinu" (For the Soviet Motherland) is based on the events. Antikainen is played by Oleg Zhakov. He also took part in the investigation of the Kuusinen Club Incident in 1920, and the suppression of the Kronstadt Rebellion a year later. After working as a lecturer in the Red Officer School, Antikainen was transferred to the Communist International in 1924. Since 1926 he gave lectures at the International Lenin School in Moscow.