Casillas made his Primeira Liga debut on 15 August, keeping a clean sheet in a 3–0 win over Vitória de Guimarães at the Estádio do Dragão. On 29 September 2015, he overtook Xavi to become the player with the most appearances in the Champions League, making his record 152nd Champions League appearance in a 2–1 home win over Chelsea. That season, Casillas also broke Edwin van der Sar's record for the most clean sheets in Champions League history, keeping his 51st clean sheet in the competition on 20 October 2015, in a 2–0 win over Maccabi Tel Aviv, as his team climbed top of Champions League Group G. In January 2016, he was blamed for the away loss at Vitória de Guimarães (1–0) in the league, following a high-profile error.