With the Fort Myers Miracle, he compiled a 7-2 record with a 4.83 earned run average in the first half of the 2008 season—helping his team capture the Florida State League first-half West Division title. Guerra's first start in the second half of the 2008 season (Tuesday, July 1) was a 4-0 complete game shutout of the Tampa Yankees. He allowed only three hits, and retired 19 in a row between a first inningsingle by James Cooper and a one-out single by Andres Perez in the seventh. It marked the first shutout of Deolis’ professional career. For the second half, he went 4-7 with a 6.08 ERA in 13 starts.
The Miracle again captured the first half division title in 2009, this time in the FSL's newly realigned Southern Division, and Guerra, again, saved his best start of the season for the second half. July 3 was Fireworks Night at Hammond Stadium, and in front of the packed house, Guerra brought a no hitter into the eighth inning against the Charlotte Stone Crabs. With one out, Christian Lopez broke it up with a double down the left field line. Guerra was promoted to the New Britain Rock Cats immediately after this game (July 7). He was named FSL pitcher of the week for the week of June 29 through July 5. His combined record for Fort Myers and New Britain was 12-11 with a 4.89 ERA and 106 strikeouts.
On November 20, 2009, he was added to the Twins' 40 man roster. He began the 2010 season with New Britain, going 1-1 with a 3.07 ERA in five starts prior to being promoted to triple-A.