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7/9/2013 12:27 A.M. ET

Harden making progress in rehab process

ST. PETERSBURG -- Twins assistant general manager Rob Antony cautioned the news with a "knock on wood," but it appears right-hander Rich Harden is once again making progress in his lengthy recovery from right shoulder surgery.

Harden is set to throw live batting practice this week, according to Antony, and has felt no soreness in his lat, forearm, shoulder or anywhere else that's been a problem lately.

"There have been no setbacks this go-round. Everything's felt good. Every report, every time he's thrown a bullpen or done anything, it's been positive," Antony said. "So hopefully he can continue to progress."

The Twins' hope for Harden, Antony said, is that he'll be healthy and built up enough to pitch out of the bullpen for Minnesota this season.

"As the season's gone on, it becomes more of a struggle to try to do that. I guess the positive is that, if we can get him out there in the [Gulf Coast League] games and he feels good, we're looking at it [from] a reliever perspective," Antony said. "So if he can pitch an inning or two, then hopefully if he can back up and have three, four good outings, progress on and maybe move him up. Then get him to the [Class A Advanced Fort Myers] Miracle or something, then Triple-A -- yeah, that's the hope, is that maybe sometime this season he could come up and we could see where he's at facing Major League hitters."

The Twins signed Harden to a Minor League deal in December and would like to get a sense of what he can bring to the table this year since he'll be a free agent this offseason. But at this point, worrying about whether Harden can compete for a job on the 2014 Twins would be looking a little too far ahead.

"Right now, we're just trying to get him where he can throw live BP, get into games and not have any setbacks or any soreness," Antony said. "If he's healthy, then we can go from there."

Walters accepts designation to Minors

ST. PETERSBURG -- Right-hander P.J. Walters has decided to stay in the Twins organization, accepting an outright assignment to Triple-A Rochester on Monday after being designated for assignment last Thursday.

Walters, 2-5 with a 5.95 ERA in eight starts for Minnesota this season, cleared waivers and had the option to become a free agent, but he instead chose to go back to Triple-A with the hope of being called up to rejoin the Twins at some point this season.

"He had a lot of good things to say about the way he was treated and how he has been treated over the two years. Wanted to stay with the organization," assistant general manager Rob Antony said. "He thought about it, and obviously he has the questions that anybody would ask. 'What's the situation? Do you think I have a chance to come back up or are you guys going to go young and bring up some of the younger guys?'

"I said there's no crystal ball, there's no guarantees, but go down there, get an opportunity to pitch, and if you're the guy, just like earlier this year, you might get a chance to come back up."

Walters will report to Rochester on Tuesday, and Antony said he hopes to make a start before the club's All-Star break from July 15-17. The 28-year-old has spent parts of five seasons in the Majors, posting a 6-10 record and 6.28 ERA in his career.

"There's a couple guys that are pitching fairly well down [in the Minors] right now that I would say probably would be ahead of him if we had to make a move tomorrow. But we'll just send him out," Antony said. "We've got some guys that are doing all right down there."

Manager Ron Gardenhire said Walters is "not necessarily" buried so far down on the Twins' depth chart that he won't get called up again. As Gardenhire put it, "We always go with who's throwing the best," should the need for a spot starter arise.

"We were disappointed when we had to make the move in the first place, because we like the guy an awful lot," Gardenhire said. "As we told him, 'We know we've got to do this. Hopefully you'll make it through for our benefit and you would accept. We would love to keep you.'

"I think he knows he'll get a chance again. We've given him the opportunity a couple times. We like him, and we were hoping it would work out for us that we got to keep him. And fortunately for us, he wanted to stay. We're happy about that."

Reliever Thielbar's scoreless-innings streak ends

ST. PETERSBURG -- Lefty reliever Caleb Thielbar entered Monday's series opener at Tropicana Field with a streak of 19 2/3 scoreless innings, the longest active mark in the Majors, and he extended that streak to an even 20 innings with a big strikeout against Luke Scott with a runner on third in the seventh inning.

He hadn't allowed a run in 17 appearances, setting the Twins record for most consecutive scoreless appearances to start a Major League career. He hadn't even allowed a hit in nearly a full month. The last one was an infield single by Washington's Jeff Kobernus on June 9.

But those streaks couldn't last forever. Unfortunately for Thielbar and the Twins, they ended in a critical situation in Monday's 7-4 loss to the Rays, with Thielbar serving up a two-run homer to Rays second baseman Ben Zobrist.

"It's not going to change who I am. I'm not going to magically become a new pitcher overnight," Thielbar said. "I'm still going to go up there and attack hitters, throw strikes every night out. As far as that goes, nothing's going to change.

"It's not like I haven't dealt with it at every level. Basically just do the same thing that I did there. Tomorrow's a new day, so hopefully I'll get put into the same situation tomorrow, except for obviously we'd like to have the lead tomorrow."

Still, the rookie has a 0.45 ERA after 18 big league outings. What's been the key to his success? According to manager Ron Gardenhire, it's been a combination of Thielbar's great stuff, his ability to hide the ball and opposing hitters' lack of familiarity with him.

"People don't know him still. That's an advantage for a pitcher. Haven't seen a lot of him," Gardenhire said. "But [his] stuff, he comes right at you. He's flinging the ball. He hides the ball. He's got a nice little breaking ball. He can cut his fastball. He throws a nice little slider. Just looks like, to me, he hides the ball very well and, typical of a lefty, with a little bit of funk. He surprises people.

"We haven't seen teams really get a chance to face him more than one time right now, and that bodes well."

Worth noting

• Outfielder Darin Mastroianni, on the 60-day disabled list with a left ankle stress reaction, is now working out in Fort Myers, Fla., with the Twins' Gulf Coast League affiliate. Mastroianni hasn't begun a Minor League rehab assignment yet, however. Antony said the outfielder is just working out and getting prepared to get back into game situations.

• Oswaldo Arcia was back in the Twins' lineup on Monday, batting sixth and playing left field. Gardenhire said Arcia (right hand bruise, knee soreness) could have played on Sunday "if we really needed him to."

"He was fine, though," Gardenhire added. "His knee was a little sore from that funny play at home plate at home the other day. Good day. He had a little bit of a break, then get him back out there."

Arcia went 1-for-4 in Monday's 7-4 loss, and was thrown out trying to stretch his single to a double in the fourth.

• Right-hander Nick Blackburn, working his way back from right wrist surgery, threw five innings for the GCL Twins on Monday. Blackburn gave up two runs on six hits and struck out five.

"Felt good, so that's all positive," Antony said about Blackburn.

• Antony said Alex Meyer, the Twins' No. 3 prospect according to MLB.com, is scheduled to begin an interval throwing program on July 16, which would put him back in games in early August.

• Right-hander Cole De Vries was placed on the seven-day disabled list at Triple-A Rochester with a right elbow strain.

Adam Berry is a reporter for MLB.com. Follow him on Twitter at @adamdberry. This story was not subject to the approval of Major League Baseball or its clubs.