Pineda signed with the Seattle Mariners at age 16 on December 12, 2005.[1] He made his professional debut with the Mariners of the Rookie-level Dominican Summer League (DSL) in 2006, pitching to a 2–1 win-loss record with a 0.44 earned run average (ERA), allowing only one earned run all season. In 2007, he had a 6–1 record with a 2.29 ERA in regular action for the DSL Mariners. Pineda pitched for the Class-A Wisconsin Timber Rattlers of the Midwest League in 2008 and had a 8–6 record with a 1.95 ERA.
Opponents had a batting average of .216 against Pineda. He led the Seattle farm system in ERA, opponent average and strikeouts (128). He was fourth in the affiliated minors in ERA behind Madison Bumgarner, Jon Kibler and Chris Cody. Pineda finished second in the Midwest League in ERA behind Kibler. He was left off the Midwest League All-Star team in favor of Alfredo Figaro. Baseball America rated Pineda as the Mariners' tenth best prospect[2] and was named Mariners Minor League Pitcher of the Year.










