Two days later, on 20 August 2005, Picken made his Chesterfield debut, where he made his first start for the club and played 90 minutes, in a 4–1 loss against Oldham Athletic. Subsequently, his loan spell with Chesterfield was extended until the end of the season despite playing nine matches. After extending his loan spell at Chesterfield, Picken then established himself in the first team and scored his first Chesterfield goal on 1 April 2006, in a 3–1 loss against Nottingham Forest. He later finished the 2005–06 season, making thirty–two appearance and scoring once.