Illarramendi netted his first league goal for the "Merengues" on 22 February 2014, after his long-range effort against Elche was deflected and the hosts won it 3–0. His second came on 5 April, as he scored the first in an eventual 4–0 victory at former team Real Sociedad in the 44th minute; he was a regular in the domestic cup campaign, coming on as a late substitute for Ángel Di María in the 2–1 final defeat of FC Barcelona, adding 11 appearances – five starts – in the team's Champions League run but remaining on the bench as they clinched the trophy against Atlético Madrid in the final at the Estádio da Luz.