"It's pretty cool -- I'm excited," Tonkin said. "[Spring Training] went good. My arm feels good. So yeah, I'm happy about it."
Tonkin, 24, is regarded as one of the club's top relief prospects, and didn't allow a run in 8 1/3 innings this spring. He also posted a 0.79 ERA in 11 1/3 innings as a rookie last season, as well as a 3.47 ERA with 66 strikeouts in 57 innings between Double-A and Triple-A.
Twins manager Ron Gardenhire said he feels comfortable using Tonkin in any situation until Duensing returns on Thursday.
"I'm not worried about him," Gardenhire said. "He's a guy we talked about keeping during Spring Training, but the numbers just didn't work out. He'll be there until we get Deuce back. But I don't worry about the kid. He can wing it."
Duensing, meanwhile, attended the birth of his second child with his wife, Lisa, on Monday in Omaha, Neb. Duensing's wife gave birth at 9:19 a.m. to a healthy baby boy named Boston Matthew, who weighed in at 6 pounds, 6 ounces.
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.