A month after joining Twente, having appeared as an unused substitute in the previous two matches, Tiendalli made his debut as a substitute for Dario Vujičević in the 63rd minute of a 3–1 win over Heracles Almelo. A week after his debut, he scored his first goal and provided an assist for Miroslav Stoch's opener in a 4–0 win over FC Groningen. Having established himself in the first team, he competed with Slobodan Rajković and Nicky Kuiper in the defence, though he also played in other positions. Tiendalli helped Twente keep four consecutive clean sheets between 17 January 2010 and 3 February 2010. Having missed out on the club’s earlier matches in Europe, Tiendalli made his Europa League debut, playing in both legs against Werder Bremen in which Twente lost 4–2, resulting in their elimination in the second round. A month later, on 16 March 2010, he signed a one-year contract extension with Twente. Tiendalli later helped the club to their first-ever Eredivisie title. By the end of the 2009–10 season, he had made thirty-two appearances, scoring once, in all competitions.