General Prezan commanded the 4th Army Corps in 1915-1916, and then became head of the Romanian Fourth Army during the Romanian Campaign later in 1916, against the forces of the Central Powers. Prezan led the Romanian Armed Forces in the Battle of Bucharest (November–December 1916), and as those forces retreated into the northeastern part of Romania (Moldavia). In July and August 1917, Prezan, who was by then Chief of the General Staff (and assisted by the then-Lieutenant-Colonel Ion Antonescu) successfully stopped the German invasion led by Field Marshal August von Mackensen. He continued serving in this position until 1920.