In his first pro start, Nallen finished T-49 at the 2004 Buick Championship. In October 2004, he Monday-qualified for the Gila River Classic at Wild Horse Pass Resort on the Nationwide Tour by shooting a round of 63.[4] He shot 60 in the first round and led wire-to-wire for his first pro win.[4] He was the 17th Monday qualifier to win, the 10th player to win in his first career start and the 19th player to lead wire-to-wire.[4] He was the first player to accomplish all three feats simultaneously.[5] He has played on the Nationwide Tour since that win.