He finished 2005 with a single start for the Triple-A Buffalo Bisons in which he was credited with a win. He was named the Indians Minor League Pitcher of the Year (Bob Feller Award) for the 2005 season. Baseball America named him the #2 prospect in the Indians organization, the #6 prospect in the Carolina League and the #8 prospect in the Eastern League. He was named the Indians' 2005 Minor League Player of the Year (receiving the "Lou Boudreau Award"). In , he was a non-roster invitee at the Indians' spring training, but did not make the club's Opening Day roster, beginning the season with Buffalo. In 15 starts for the Bisons, he picked up where he left off in 2005, posting a sterling 9–1 record and 1.39 ERA. Baseball America named him the #3 prospect in the International League. Major leagues Sowers' performance for Buffalo in 2006 earned him a promotion to Cleveland on June 20 where he made his major league debut against the Reds on June 25, taking the loss (5 IP, 4 ERs, 5 Hs, 2 HRs, 3 SOs, 2 BBs). He tossed his first major league complete game shutout on July 22, , against the Minnesota Twins, allowing 4 hits and 1 walk while striking out 4. Six days later, he threw another shutout—this one a 1–0 game against the Seattle Mariners—becoming the first Indians rookie to throw back-to-back shutouts since Dick Tidrow in . In his next start against Boston, he extended his scoreless inning streak to 22 before yielding an RBI double in the fifth inning. Sowers was projected to be the Indians' fourth starter in . When Cliff Lee was injured during spring training, Sowers was bumped up to the third spot in the starting rotation. However, he struggled through the first two months of the season (1–6, 6.93 ERA in 12 starts) and was demoted to Buffalo on June 10. During spring training in 2009, Sowers competed for the fifth starting pitcher slot; he was not selected and was sent down to the Triple-A Columbus Clippers. On March 31, 2010, after failing to secure a spot in the major league starting rotation, Sowers was sent outright to Triple-A Columbus and removed from the Indians' 40-man roster. Suffering with a sore shoulder for most of the season, Sowers was finally placed on the disabled list on August 14, 2010 and did