"I don't think anybody really trusted that I was healthy," the outfielder said. "I could've easily sat on the DL all year. I wanted to fight my way back, and I did."
Mastroianni began 2014 with the Twins, but he was designated for assignment after playing in just seven games. The Blue Jays claimed him off waivers and sent him to Triple-A Buffalo, where he batted .290 with 14 steals and an on-base percentage of .376 before being called up to the Majors on Wednesday.
"If I had to pick a team, I don't think Toronto would've been first on my list with the depth of outfielders they have here," Mastroianni said.
Mastroianni was not in the lineup on Thursday against the Orioles in Baltimore, but manager John Gibbons planned to use him in a similar way as outfielder Kevin Pillar was before being sent down on Wednesday.
"He'll come in and face some lefties for [outfielder Anthony] Gose, that kind of thing," Gibbons said. "He can pinch-run, do a lot of those things. He'll do a lot of what Pillar was doing."
This is Mastroianni's second stint with the Blue Jays. His first came in 2011, when he made his MLB debut for a team that finished fourth in the AL East.
Most of the faces Mastroianni encountered in the clubhouse were different -- Jose Bautista and first baseman Adam Lind were some of the few he knew from the last time around -- but the bigger change for him will be playing for a first-place team for the time in his career.
"It's exciting for me; I've always felt my role on a team was to help teams win," Mastroianni said. "When you're in first place by five games, the pressure's a little bit higher for you."
David Wilson is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.