Tiendalli made his Swansea City debut in the third round of the League Cup, providing an assist for Danny Graham in a 3–2 win over Crawley Town. Having been on the bench in the league for two months since joining, as a result of Ben Davies and Àngel Rangel being first choice in the left and right back position respectively (Tiendalli played in both positions), he finally made his league debut on 1 December 2012 against Arsenal, coming on as a substitute for Jonathan de Guzmán in the 74th minute of a 2–0 win. After the match, Tiendalli stated his intent to stay at Swansea despite his lack of first-team opportunities. From December, he became the club’s first choice right-back after Rangel was injured, as well as being rotated in different positions. Tiendalli appeared in the final of the League Cup when he came on for Davies in the 84th minute of a 5–0 win over Bradford City, Swansea becoming the first non-English Premier League team to win the League Cup and the first since 1927 to win a major English cup (Swansea's rivals Cardiff City won the FA Cup in 1927). Manager Michael Laudrup praised Tiendalli for his performance in response to uncertainty over his future. Laudrup, however, said he expected Tiendalli to move on at the end of the season. Tiendalli scored his first goal for the club in a 3–2 away win over Wigan Athletic on 7 May 2013 at the DW Stadium. In his first season at Swansea City, he made twenty-one appearances and scored once in all competitions. At the end of the 2012–13 season, Tiendalli's agent Sebastien Casenaz told talkSPORT that he would not be at Swansea the following season after contract talks had broken down.