Bornstein was selected by Chivas USA in the fourth round (37th overall) at the 2006 MLS SuperDraft. A forward in college, he was converted to a left back by Chivas coach Bob Bradley, and was his team's surprising starter at the position when the season opened. Injuries and suspensions forced Bornstein back into an attacking role for Chivas USA's June 3 match against FC Dallas, where the rookie scored his first MLS goal. He continued his fine play in the back and also contributed to the attack during the rest of the season, finishing the year with four assists and six goals, leading all rookies. He started every game in the season, and his total of 2,878 minutes played was third-highest in the league. He was rewarded for his fine form by winning the 2006 MLS Rookie of the Year Award.