In 2002, Guzmán went 5–2 with a 1.89 ERA for the Lansing Lugnuts and 6–2, 2.39 with the Daytona Cubs. He was the #13 prospect in the Midwest League and #11 in the Florida State League according to "Baseball America". In 2003, he went 3–3 with a 2.81 ERA for the West Tenn Diamond Jaxx, striking out 87 and walking 26 in 90 innings of work. He was rated the ninth-best prospect in the Southern League and picked to perform in the All-Star Futures Game, but was unable to do so when he injured his right shoulder, cutting his year short. In 2004, he had a 5.60 ERA and 0–3 record for West Tenn and 3–1, 4.20 for Daytona in a total of 11 starts. In 2005, he pitched in four games for the AZL Cubs (with 17 strikeouts and one walk in 12 innings pitched) and two for the Peoria Chiefs.