Another three days later, on 24 July, Díaz scored his first goal for his new team during the return leg against Flora Tallinn. It was a direct free kick and it was the final goal in the teams 3–0 win. 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 he won the Championship title with the team. In the 2012–13 Swiss Cup Basel reached the final, but were runners up behind Grasshopper Club, being defeated 4–3 on penalties, following a 1–1 draw after extra time. Basel had started in the 2012–13 UEFA Champions League in the qualifying rounds. But were knocked out of the competition by CFR Cluj in the play-off round. They then continued in the 2012–13 UEFA Europa League group stage. Ending the group in second position, Basel continued in the knockout phase. Winning in the round of 32 against Dnipro Dnipropetrovsk, Basel were matched against Zenit St. Petersburg in the round of 16. Following a 2–0 home win, the second leg was played in the Petrovsky Stadium. The home team took a goal lead in the 30th minute and after his second yellow card in the 44th minute Diaz was dismissed, but Basel held the result and advanced. Beating Tottenham Hotspur in a thrilling quarter-final, 4–4 on aggregate then 4–1 on penalties, Basel advanced as far as the semi-finals, there being matched against the reigning UEFA Champions League holders Chelsea. Chelsea won both games advancing 5–2 on aggregate, eventually winning the competition. At the start of their 2013–14 season season Díaz was member of the Basel team that won the 2013 Uhrencup, beating Red Star Belgrade in the final. Basel joined the 2013–14 Champions League in the qualifying rounds and they advanced to the group stage. Finishing in third place in their group, Basel qualified for Europa League knockout phase and here they advanced as far as the quarter-finals. But eventually they were beaten by Valencia 5-3 on aggregate, after extra time. At the end of the 2013–14 Super League season Díaz won his second league championship with Basel. The team also reached the final of the Swiss Cup on 21 April 2014. Gastón Sauro and Giovanni Sio were both sent off as Basel fell to rivals FC Zürich 2–0