MINNEAPOLIS -- Darin Mastroianni made his debut with the Twins on Thursday, starting in left field and batting eighth against the Blue Jays.

Mastroianni was recalled from Triple-A Rochester when third baseman Danny Valencia was optioned to Rochester after Wednesday's game.

It marked the 26-year-old's second career start, as he made his Major League debut with the Blue Jays, coincidentally, on Aug. 24, when he went 0-for-2. Mastroianni was claimed off waivers by the Twins from the Blue Jays on Feb. 9.

"This is like a dream come true to me," Mastroianni said. "Obviously coming over to the Twins this offseason was a big deal, changing teams for the first time. Everyone's been real nice and really supportive and helpful from Day 1. I'm just really excited to be here. To get that call last night was a big deal. It's a big moment in my career."

Mastroianni began the season at Double-A New Britain, batting .143 with one double in nine games, before being promoted to Rochester on April 14. In 19 games with the Red Wings, he hit .346 with two doubles, two triples and 10 stolen bases.

"He's been playing well down there and running all over the place, and I want to see him out there, see what happens," Twins manager Ron Gardenhire said. "He's been getting it done. That's why he's up here. We talked about the guys who were playing the best."

Walters joins club, will start Saturday

MINNEAPOLIS -- Right-hander P.J. Walters joined the Twins at Target Field on Thursday and said he's looking forward to making his first start on Saturday.

Walters, 27, had his contract purchased from Triple-A Rochester on Wednesday after left-hander Matt Maloney was designated for assignment.

Walters made six starts with the Red Wings, posting a 2.70 ERA with 25 strikeouts and six walks. Saturday will mark his fifth career big league start, as he has a career 7.24 ERA in 20 games with the Cardinals and Blue Jays.

He said he heard of the news late Wednesday, when Triple-A manager Gene Glynn called him to tell him he'd be joining the Twins rotation with left-hander Francisco Liriano headed to the bullpen.

"Obviously, I was excited," Walters said. "He just kind of told me I was going up and pitching on Saturday, so make the most out of the opportunity."

Walters, who said he throws a fastball, cutter, curveball and changeup, said he hopes his big league experience will serve him well, but that he always gets butterflies before every start.

"There's nerves, even in Triple-A, there's nerves," Walters said. "You care about what you're doing, you try to win. It doesn't matter where you're pitching."

Liriano frustrated, but understands move to 'pen

MINNEAPOLIS -- Left-hander Francisco Liriano said he's been frustrated by his slow start this season and understands why the Twins decided to move him to the bullpen to try to get him back on track.

In six starts, Liriano posted a 9.45 ERA with 21 strikeouts, 19 walks and six homers allowed over 26 2/3 innings. Right-hander P.J. Walters will take his place in the rotation and start Saturday against the Blue Jays.

"I've been there before, so I have to go out there and try to do my job," Liriano said. "I'm happy to be here and try to do anything to help the team win some ballgames. Either from the bullpen, starting, whatever I have to do."

Gardenhire said the club debated whether to option him to Triple-A Rochester, but decided it wouldn't do him any good to face inferior hitters in the Minor Leagues.

"We need him to face Major League hitting and bear down and get some Major League hitters out," Gardenhire said. "I'm not talking about a period of time here we'd like to see him maybe get out there. Who knows? I'm not going to put it in days, but he needs to face Major League hitters. He needs to get through that."

Liriano added he's healthy, but is disappointed with the way the season has gone, as he dominated in Spring Training with a 2.33 ERA with 33 strikeouts and five walks in 27 innings.

"It's been tough, to be honest," Liriano said. "Having the spring that I had and coming into the season then walking so many guys and getting behind in the count, it's kinda tough for me. It has been up and down but I gotta find a way to get back to pitching better."

Carroll gets first day off of season

MINNEAPOLIS -- Infielder Jamey Carroll sat out for the first time this season on Thursday, as Trevor Plouffe started at third base and Alexi Casilla returned to second base after missing three games with a sore shoulder.

Carroll, 28, is batting .218 with a .312 on-base percentage so far this season. He's expected to see time at second base, shortstop and third base moving forward.

"The trainers came in and said he's never going to say he needs a day off, so you're going to have to make the decision one of these days to give him a break," manager Ron Gardenhire said. "And that was an easy decision for me. I've been trying to get a situation where we can do that. I've got enough infielders up here now where he can get a break. He's played pretty much every inning."

Plouffe, meanwhile, made his second start of the season at third base, as third baseman Danny Valencia was optioned to Triple-A on Wednesday. But Gardenhire said he'll use a rotation of players at third in Valencia's absence.

"I'm not going to sit here and say he's every day there," Gardenhire said. "We're going to mix all these guys around. I've got to use them all."