The 27-year-old, who has 78 games of big league experience over the past two seasons, walked twice, stole a base and scored a run Sunday in the Twins' 7-4 loss to a Pittsburgh Pirates' split squad.
"Walks, hits, whatever it takes for me to get on base," he said. "At the end of the day, I don't really care too much about the batting average. I care more about my on base percentage. Today was a good day. On base two out of the four at-bats."
Mastroianni is hitting .375 (6 for 16) with a .444 on-base percentage
"That's part of my game to help us be successful and win," he said. He stole 21 bases in 77 games last year for the Twins and swiped 14 more during 29 games in the minors.
Aaron Hicks may be the leading candidate for center field. Manager Ron Gardenhire said he hasn't made a decision.
"Hicksie is doing great," Gardenhire said.
Hicks was 1 for 2 with a walk, RBI and run. The leadoff hitter had a three-homer game against Philadelphia on Thursday.
"Gardy is going to make that decision in three weeks," Mastroianni said. "In three weeks I'll either be on that flight to Minnesota or I won't be. And then whatever roles it is I'll be ready for it and prepared to be the best for that role. It's about winning about baseball games."
"Wind blowing out," Gardenhire said. "That's what happens."
Jonathan Sanchez, in his first spring training start and fourth appearance, gave up two runs and two hits in two innings. Sanchez has an 11.81 ERA in 5 1/3 innings during the exhibition season.
Minnesota's Liam Hendricks, making his fourth spring training start, allowed four runs and three hits in three innings.
The Twins reassigned five players to their minor league camp: RHP Bryan Augenstein, RHP Nick Blackburn, RHP Alex Meyer, RHP Lester Oliveros and RHP Esmerling Vasquez. ... Twins 3B Trevor Plouffe tweaked a calf muscle Sunday in agility drills. Gardenhire said he's not sure when Plouffe will return.