Duensing was drafted by the Minnesota Twins in the 3rd round of the 2005 Major League Baseball draft. After he was drafted, he played for the rookie team Elizabethton Twins, going 4–3 with a 2.32 ERA and striking out 55. In , he went 5–10 in 28 games with a 3.49 ERA with 3 teams, the AA New Britain Rock Cats, A Fort Myers Miracle and A Beloit Snappers. In 2007, he played part of the season with the Rock Cats going 4–1. He was then promoted to the Triple-A Rochester Red Wings, where he went 11–5 with 3 complete games, 3.24 ERA and 86 strikeouts for the rest of the season.
