After progressing through the ranks at the club, Tiendalli was called up to the first team for the first time in December 2004. He made his debut as a 75th-minute substitute in a 1–0 win over Den Bosch on 19 December 2004. Tiendalli found himself in and out of the starting line-up, also playing in the reserve team. Tiendalli scored his first sernior goal for FC Utrecht, having come on as a 73rd-minute substitute, in a 1–0 win against RBC Roosendaal on 12 February 2005. By the end of the 2004–05 season, he had made eleven appearances and scored once in all competitions. Following this, the club began talks over a new contract.