 He scored his first league goal for them during the 2–1 away win in the Stade Olympique de la Pontaise against Lausanne-Sport on 17 February 2013.At the end of the Swiss Super League season 2012–13 Díaz won the Championship title and was Swiss Cup runner up with Basel.In the 2012–13 UEFA Europa League Basel advanced as far as the semi-finals, there being matched against the reigning UEFA Champions League holders Chelsea, but they were knocked out, losing both home and away tie, beaten 2–5 on aggregate.