Berglund wasted little time establishing himself as a productive NHL player. He was named to the NHL All-Rookie Team in 2008-09 after he had 21 goals, becoming the 10th rookie in St. Louis Blues history to score 20. Among those goals was the 10,000th in franchise history, Nov. 1, 2008, against the Pittsburgh Penguins.
Selected by the Blues with the No. 25 pick in the 2006 NHL Draft, Berglund was fourth among NHL rookies with 47 points and second in power-play points (22). He led the Blues with a plus-19 rating, second among rookies, and played in the YoungStars game that season.