While there were doubts over whether Casson would be able to hold down a permanent place in the New South Wales team with four other spinners in the squad, he managed to play seven matches in his first season with the Blues. Despite this, he had a very poor first season, taking only 7 wickets at an average of 72.00, however his form was not helped by a shoulder injury that eventually required reconstructive surgery. Coming back from shoulder injury, Casson had an excellent 2007-08 Pura Cup season. Playing nine matches in the season, he took 29 wickets at an average of 35.13 and scored 485 runs at 60.62. He hit a career top score of 99 off 180 balls against South Australia at the Sydney Cricket Ground and he played a vital role in the Blues' 2007-08 Pura Cup final win. After scoring 89 in a state record seventh wicket stand with Brett Lee, he took 4 wickets in Victoria's unsuccessful run chase, including the final wicket that won the Cup for New South Wales. His strong season was rewarded with his first Cricket Australia contract on 9 April 2008.