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5/15/2014 1:36 P.M. ET

After successful BP, Willingham heads to Triple-A

MINNEAPOLIS -- Twins left fielder Josh Willingham took batting practice without any issues before Thursday's game against the Red Sox, and is set to begin his rehab assignment at Triple-A Rochester on Friday.

Willingham hit on the field before the game, and reported no problems with his left wrist. Willingham, who is on the 15-day disabled list with a small fracture in his left wrist, retroactive to April 7, was scheduled to fly out to Rochester after Thursday's game.

"Willingham was out on the field this morning and everything went well," Twins assistant general manager Rob Antony said. "He was hitting bombs. He looked good. So he'll head to Rochester this afternoon."

There's still no exact timeline for his return, as he needs plenty of at-bats, considering he hasn't played in more than a month.

"It's twofold," Antony said. "You want to make sure he's healthy and his timing is down and is swinging well before he gets back. We haven't really put a timetable on him. If it's up to him, it would be two or three days, but I don't think that's realistic. He needs more time."

Colabello back in starting lineup on Thursday

MINNEAPOLIS -- After a hot month of April, Chris Colabello has cooled off in May. But he was given the start on Thursday against the Red Sox, his first since Sunday.

Colabello hit .295/.343/.484 with three homers and 27 RBIs in 24 games in April, but entered Thursday batting .149/.200/.234 with one homer and three RBIs in 13 games in May.

Twins manager Ron Gardenhire said he believes Colabello got worn out from playing every day, including 16 starts in right field for the natural first baseman. Colabello made his 12th start at first base on Thursday, with Joe Mauer serving as designated hitter.

"I think he needed [a break], because we pressed him to the limit and played him an awful lot, so I think he got a little worn down," Gardenhire said. "We used him as a pinch-hitter the last few days. But he has a great attitude."

Gardenhire added that Mauer is feeling much better after dealing with lower back issues last week, but he just felt like Thursday was a good day to get Colabello at first base and allow Mauer to take a day off from playing first.

"Any time you can get a chance like this and you can move some guys around and back problems are never easy to deal with," Gardenhire said. "But he's feeling great and he's doing fine. But I just wanted to get Colabello on the field."

Twins seek consistency from Tonkin

MINNEAPOLIS -- Twins manager Ron Gardenhire wants to see more consistency from rookie reliever Michael Tonkin, who has struggled in recent outings.

Tonkin, who remains one of the club's top relief prospects, has a 6.35 ERA in 14 appearances, with eight strikeouts and six walks in 11 1/3 innings. He's given up eight runs (six earned) in 2 2/3 innings over his last three appearances, including back-to-back subpar showings against the Red Sox on Tuesday and Wednesday.

Gardenhire said he wants to see Tonkin mix in more sliders, as he's throwing his fastball, that has averaged 92.7 mph, 80.1 percent of the time.

"He's overthrowing the baseball," Gardenhire said. "He's not throwing the breaking ball. You have to go out and tell him to spin the ball a little bit. You shouldn't have to tell him, but when he's not overthrowing his fastball and using his slider, he can get people out. But he's just trying to throw the ball through a brick wall right now and it's not working."

Twins assistant general manager Rob Antony agreed with Gardenhire, as he'd like to see Tonkin use his slider more to get hitters off his fastball.

"He's struggled the last few times out," Antony said. "He's trying to throw his breaking ball more, but has struggled recently after starting out well. I don't think he can just live on a fastball up here. He doesn't throw 98 mph. He's at 91 to 94-95 right now, and you have to something to take them off that baseball."

Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.