Carlsen made his breakthrough as part of Vorup FB who were competing in the lower tier Jutland Series,[3] before moving to newly formed Randers FC in 2003.
[a] He won promotion to the Danish Superliga with Randers during the 2003–04 season,[4] and made his professional debut in the top tier on 1 August 2004 starting in a 1–0 home loss to Herfølge Boldklub, before coming off in the 76th minute for Kim Østergaard Nielsen.
[7] After relegation, Carlsen was often injured and moved down the depth chart as Peter Christiansen was preferred at left-back by head coach Lars Olsen.
[9][10] He made his European debut for Valur as they lost 2–0 to Cork City on 23 June 2007 in the UEFA Intertoto Cup first round.
[8] Despite lacking top-level speed, he compensated with good positioning and a fine skillset which made him a strong crosser of the ball.