Christensen joined Danish Superliga club FC Nordsjælland in 2004, competing with Japanese international Yoshi Kawaguchi for the starting position.

[4] He played all 33 league games as Nordsjælland finished in 10th place in the 2004–05 season, and also saw off the competition from backup keeper Jan Budtz.

Copenhagen, Christensen made an uncharacteristic mistake as Nordsjælland lost 1–0, when he mistimed a kick of the ball, leaving it rolling into the empty net.

Christensen transferred to IFK Göteborg on 13 March 2008, as a replacement for club legend Bengt Andersson, who had retired after the previous season.

[12] On 21 September 2008, Christensen won his second title with the club when Kalmar FF were defeated in the 2008 Swedish Cup final on penalty shootout, after drawing the game 0–0.

During the autumn 2012, Johan Wiland was kept out in two longer periods with injuries,[20][21] whereas Christensen played 16 full matches, including four games in the UEFA Europa League group stage.

[23] Christensen made his first international appearance, when he joined the Denmark League XI national football team for unofficial games at the 2009 King's Cup in January 2009.

After joining IFK, Christensen was called up for the Danish national team in September 2008, to replace the injured Thomas Sørensen and Jesper Christiansen,[24] but did not play.