BALTIMORE -- Left-hander Pedro Hernandez arrived in Baltimore on Saturday, but won't be activated until Sunday morning before his 12:35 p.m. CT start against the Orioles.
The Twins will place right-hander Cole De Vries on the 15-day disabled list, retroactive to March 30, with a strained right forearm to make room for Hernandez on the roster.
Hernandez -- who will make his Twins debut, but has one big league appearance with the White Sox under his belt -- said he found out from Triple-A Rochester manager Gene Glynn on Friday that he would start for Minnesota.
"I was in shock when Gene told me that I was going to the big leagues and going to start on Sunday," Hernandez said. "I said, 'What, are you kidding?' And he said, 'No,' and, 'Congratulations.' So I thanked him. It's exciting. I'm here and I'm ready."
Hernandez, who was acquired along with infielder Eduardo Escobar in the trade that sent Francisco Liriano to the White Sox before last year's Trade Deadline, will be making his second career start. He made a spot start for Chicago against the Red Sox last year and gave up eight runs in four innings.
But he fared better in the Minor Leagues with a combined 3.32 ERA between Double-A and Triple-A in two organizations last season, and excelled this spring with 11 scoreless Grapefruit League innings.
"It's going to be entertaining," Twins manager Ron Gardenhire said. "He had a good spring. We used him out of the 'pen. I think he made only one start, but he mostly came out of the bullpen. But he's a starter and has a good changeup and has a good fastball he can cut and a nice looping curveball."
Hernandez was scheduled to start for Rochester on Sunday, and Gardenhire said the lefty will likely throw about 75-85 pitches.
Hernandez said his wife, Jackie, and his daughter, Bianca -- born the same day he was traded to the Twins -- will be in attendance to watch him start. He said his goal is to impress Twins management and stick in the rotation, but that could be tough, as left-hander Scott Diamond is on track to return to the rotation Friday against the Mets.
"I'm going to try my best," Hernandez said. "And try to stay here all year."
Mastroianni remains sidelined by bruised ankle
BALTIMORE -- Outfielder Darin Mastroianni remains bothered by a bruised left ankle and still isn't ready to play nine innings just yet.
Mastroianni, who injured his ankle on a foul tip in a March 25 Spring Training game, has appeared in two games entering Saturday's matchup with Baltimore, but has yet to make a start in the outfield. He said he reinjured his ankle trying to get loose Monday on Opening Day, but that it's getting better.
"I started my routine like I did last year to get ready to get in a game, but my ankle wasn't quite ready," Mastroianni said. "I woke up Tuesday in quite a bit of pain. Wednesday was pretty painful. But we tailored the program to use a bike. So the last four days it's been getting significantly better."
He said his goal is to be ready to start in a game against the Royals this week, but it remains more likely he'll make his first start against the Mets next weekend.
"It's a tough spot," Mastroianni said. "I want to get in there as soon as I can. We have a few guys who could use a day here or there, but I'm not ready to do that yet. But at the same time, there's still six months left, and I don't think anybody wants this to linger."
With Mastroianni unavailable to start, rookie Aaron Hicks has started the Twins' first five games in center field. He's struggled so far, entering Saturday's game against the Orioles with a .059 batting average (1-for-17), but Twins manager Ron Gardenhire said he's not worried about the slow start from the rookie.
"He's fine," Gardenhire said. "Nobody ever said this would be easy. I wish people would step back. I know there's already been a lot of talk about him already, which is silly. We've faced two of the best teams in baseball already in Detroit and Baltimore, and some of the best pitching in baseball. So he's not only getting his feet wet, he's facing some of the best pitching here, so we have to give him some slack."
Butera breaks hand in Triple-A game
BALTIMORE -- Catcher Drew Butera, who was among the Twins' final Spring Training cuts, broke his left hand while playing for Triple-A Rochester on Friday and was placed on the Minor League disabled list.
Butera, who is expected to be out three to four weeks, was hit on the hand on a pitch from Ramon Ortiz in the second inning of Friday's home opener for the Red Wings.
He played in 42 games with the Twins last year, hitting .198 with a homer and five RBIs, and entered the year third on Minnesota's catching depth chart behind Joe Mauer and Ryan Doumit.
"It's sad," Twins manager Ron Gardenhire said. "Drew is a very good catcher. He doesn't belong in Triple-A. He's a Major Leaguer. He's one of the best defensive catchers we have hitting and throwing."
Twins option Robertson to Triple-A
BALTIMORE -- The Twins optioned left-handed reliever Tyler Robertson to Triple-A Rochester after their 6-5 win against the Orioles on Saturday. They will make a corresponding roster move before Sunday's game.
Robertson allowed one run in one inning across two appearances this season. His last outing came against the Orioles on Friday, when he gave up a go-ahead grand slam to Chris Davis in the eighth inning.
The move leaves the Twins with Brian Duensing and closer Glen Perkins as the lone left-handers in the bullpen.
Right-hander Anthony Swarzak, who is on the 15-day disabled list with two fractured ribs, is the most likely candidate to replace Robertson on the roster.