On 13 September, Casillas equalled Ryan Giggs's record of playing in 19 consecutive UEFA Champions League campaigns when he appeared in Porto's 3–1 home defeat to Beşiktaş in the 2017–18 edition of the tournament. On 2 April 2018, Casillas played his 1,000th match as a professional in Porto's 2–0 loss at Belenenses. In May, he won his first trophy with the club as they won the league title for the first time since 2013. The 2017–18 Primeira Liga title was confirmed after Sporting CP and Benfica tied their respective match. On 17 May 2018, he renewed his contract with Porto for another year.