Mastny, nicknamed "Mr. Nasty", was born in
Bontang,
Indonesia, and played collegiate baseball at
Furman University, where he was primarily used as a
starting pitcher. In , he was named the
Southern Conference Pitcher of the Year, but was not widely regarded as a top-tier prospect. Mastny was selected in the 11th round (320th overall) of the
2003 Major League Baseball draft by the
Toronto Blue Jays. He began his professional career that year with the
Auburn Doubledays of the Single-A
New York–Penn League, going 8–0 with a 2.26 ERA in 14 starts. He also struck out 68 batters in innings. In , Mastny played the entire season with the Single-A
Charleston Alley Cats, going 10–3 with a 2.17 ERA in 27 starts. After beginning the season in the starting rotation of the Single-A
Kinston Indians, Mastny was converted into a relief role. He posted a 7–3 record, two saves and a 2.35 ERA in 29 games (11 starts) with Kinston before being promoted to the Double-A
Akron Aeros. Although still mostly unheralded as a prospect, due partly to his age (then 25), Mastny's career quickly accelerated that summer as the unexpectedly non-contending Indians began shuffling a bullpen that often struggled, particularly after the trade of
closer Bob Wickman. The rookie pitcher—whose role with Akron and Buffalo was almost exclusively in middle relief, and who had recorded only three
saves in the minors—was given an opportunity to close essentially by default, earning his first save with two scoreless innings against the
Tampa Bay Devil Rays on August 19. That day, manager
Eric Wedge announced that Mastny would be among those tried out in the role over the remainder of the season. He made three total appearances in the series, striking out three batters and walking two in scoreless innings, After a
spring training roster battle with
Jorge Julio and
Scott Elarton for Cleveland's final bullpen spot in , Mastny was slotted to begin the season with Triple-A Buffalo. He was recalled on April 15, 2008, when
Joe Borowski went on the 15-day
disabled list. Mastny made his first career start on June 3, 2008, against the
Texas Rangers. He took the loss, allowing five earned runs, including home runs to
Josh Hamilton and
Milton Bradley, in innings. He was optioned to Buffalo after the game. On December 7, 2008, the Indians sold Mastny's contract to the Yokohama BayStars of the Japanese
Central League. Mastny had a 1–5 record with an ERA of 5.69 in 15 games for the BayStars in 2009. ==Birthplace confusion==