ポトマック・ナショナルズ
The Washington Nationals signed Barthmaier on June 29, 2010. He finished the 2010 season with the GCL Nationals in the Gulf Coast League and the Potomac Nationals of the Carolina League. In 2011, Barthmaier pitched for the Double A Harrisburg Senators, posting a 5.05 ERA in 67 2/3 innings.