ポトマック・ナショナルズ
Martínez began in the Washington Nationals organization, commencing his professional career in 2006. That year, he played for the Vermont Lake Monsters, Savannah Sand Gnats and Potomac Nationals, hitting a combined .265 with 11 stolen bases in 82 games. In 2007, he played for the Hagerstown Suns and hit .250 with 13 stolen bases in 116 games. He played for the Potomac Nationals and Harrisburg Senators in 2009, posting a .259 batting average with 10 steals. In 2010, he played for the Senators and Syracuse Chiefs, hitting a combined .272 with 11 home runs and 23 stolen bases.