Nelson was not drafted in the 2008 NBA draft, but he was signed by the Golden State Warriors on September 9, 2008. He became the first undrafted rookie to start on opening night in the history of the NBA. On November 14, 2008, he and teammate Richard Hendrix were assigned to the Bakersfield Jam of the NBA D-League. He was recalled by the Warriors on December 16, 2008, but he was waived on January 6, 2009 to make room for Jermareo Davidson.