How did Americans save Paris in World War 1?

Americans did not save Paris in World War 1. The city was successfully defended by French and British forces in the First Battle of the Marne (September 5-12, 1914). American Expeditionary Forces troops did not begin arriving in France until June 1917. Their contributions, including the pivotal Meuse-Argonne Offensive, were certainly significant in ultimately helping the Allies secure victory on the Western Front in November 1918, but they played no part in the defense of Paris during the opening months of the war.