On 25 March 2014, Guarín agreed to extend his contract with Inter until 2017. On 14 September, as a second-half substitute, he scored in a 7–0 home win against U.S. Sassuolo Calcio. At the start of the 2014–15 season, he began being used by manager Walter Mazzarri as a second striker.
On 7 December 2014, in his 100th appearance for Inter, Guarín assisted Mauro Icardi in the 44th minute of an eventual 1–2 home defeat against Udinese Calcio. On 16 February of the following year, he scored twice after winning a first-minute penalty kick in a 4–1 success at Atalanta BC, helping his team to secure the first away win in the league since December 2014.