He played in Major League Baseball (MLB) for the Toronto Blue Jays and Minnesota Twins.

He played for the Auburn Doubledays in 2007, hitting .287 with three home runs, 26 RBI and 20 stolen bases in 68 games.

He split 2009 between the Dunedin Blue Jays and New Hampshire Fisher Cats, hitting a combined .297 with 70 stolen bases in 131 games.

[1] Mastroianni was called up to replace the newly acquired Kelly Johnson, who had to return to Arizona because he forgot his passport.

[8] Mastroianni was claimed off waivers by the Toronto Blue Jays on April 22, and was optioned to the Triple-A Buffalo Bisons.

[9] He was recalled by the Blue Jays on June 12, and sent back to Buffalo after appearing in 14 games, where he batted .156 with 1 home run and 2 RBI.

Upon his activation from the injured list on July 4, Mastroianni was removed from the 40–man roster and sent outright to the Triple–A Rochester Red Wings.