MINNEAPOLIS -- Left-hander Brian Duensing admitted he was frustrated with his results as a starter, but said he's fine with moving back to the bullpen with right-hander Nick Blackburn set to rejoin the rotation on Friday against the Royals.

Duensing fared well as a reliever to start the season -- posting a 3.12 ERA in 34 2/3 innings -- but struggled in four starts, with a 10.13 ERA in 13 1/3 innings. His last outing was his worst, as he gave up six runs over just two innings against the A's on Sunday.

"I was having a lot of success in the bullpen and had a good first half, so I'm not thinking of this as a demotion," Duensing said. "It's just a move that needs to be made and we'll go from there."

Duensing, who has a career 4.41 ERA as a starter compared to a 3.25 ERA as a reliever, added that he prefers starting, but understood Twins manager Ron Gardenhire's decision.

"If I had the preference, I'd like to start, but now is not the time to do it, unfortunately," Duensing said. "If I can continue to come out of the bullpen and get lefties and righties out and throw anywhere from one to three innings, it'll help the team out just as much."

Gardenhire said that Duensing will see some time in long relief because he's stretched out, but that he'll also be used in one-inning stints.

"We're looking for some length out there, so he'll be able to do some of those things, too," Gardenhire said. "Duensing was very good out of the 'pen. He can go left-right. And he's a guy who can stretch out for us so he'll be valuable."

Blackburn gets another chance after his struggles prompted the Twins to send him to Triple-A Rochester two weeks ago.

The right-hander went 4-5 with an 8.10 ERA in 13 starts before he was optioned to Rochester on July 4. But in two starts since for the Red Wings, Blackburn went 2-0, allowing one earned run in 15 innings.

"His first outing was outstanding," Gardenhire said. "Second outing, a few more fly balls than he normally gives up. He pitched very well, threw the ball very well. He was on top of the ball, had good sink and good command of his pitches. He's gotta come up here and do it."

Friday will be Blackburn's 13th career start against Kansas City. He enters the matchup 3-3 with a 4.73 ERA lifetime against the Royals.

Capps out indefinitely after undergoing MRI

MINNEAPOLIS -- Results from Matt Capps' MRI on Wednesday indicate the closer will likely be out longer than initially anticipated. The Twins placed Capps on the 15-day disabled list on Tuesday with rotator cuff irritation.

"It didn't come out as favorably as I was hoping," Minnesota general manager Terry Ryan said. "We're going to have to shut him down for a while."

Ryan didn't put a specific timetable on when the club thinks Capps will be able to return, but said it would be longer than a 15-day DL stint.

Capps sustained the injury during an inning of work against Baltimore on Monday. It was just his second appearance after he missed 15 games on the DL with right shoulder inflammation.

The right-hander made two rehab appearances for Class A Advanced Fort Meyers before he was activated from the DL on July 13.

"There wasn't any urgency to rush back," Ryan said. "He was doing fine on the rehab assignment. [On Monday], he did something to irritate that thing."

Capps owns a 3.81 ERA in 29 appearances for Minnesota and has successfully converted 14 of 15 save opportunities.

Robertson proving his worth in bullpen

MINNEAPOLIS -- Tyler Robertson is proving himself to be a valuable asset in the Twins' bullpen. His two big outs in Tuesday's win over Baltimore were the latest example.

Clinging to a 4-3 lead, the Twins called on Robertson with one out in the sixth and a man on first base. He induced a groundout from Nick Markakis, then the Twins elected to intentionally walk J.J. Hardy to get the left-hander working against Jim Thome, whom Robertson looked up to as a youngster.

Robertson responded with one of the biggest strikeouts of his young career, preserving Minnesota's lead.

"It was a fun situation to be in," Robertson said. "Thome was one of my favorite players growing up, so it was pretty exciting. I was ready for the challenge and it worked out."

Robertson owns a 4.70 ERA in 7 2/3 innings since being recalled from Triple-A Rochester on June 25. But he's dominated lefties, holding them to a .222 batting average and striking out nine of the 18 left-handed hitters he's faced.

"When we get in situations like this, this is where you get an opportunity," Twins manager Ron Gardenhire said. "We've had so much trouble with pitching. So he was down there, throwing the ball pretty decent, and got an opportunity. He's come up here and proven that he can get some lefties out."

It's decisions like Gardenhire's, to match Robertson up against a future Hall-of-Famer in Thome, that show the club's belief in the 24-year-old.

"I'm confident in getting those guys out," Robertson said. "Knowing that the coaching staff has that confidence in me to go get those guys is a big boost."