 The next season, Díaz made his professional debut in a 3–2 loss with Everton for the first week of the 2005 Apertura Tournament.In the 2006 season, he played 29 matches between the Apertura and the Clausura Tournament.After the one season, in the Apertura Tournament 2008, Díaz was a frequently starter in the squad of Arturo Salah, and scored his first professional goal with the club on 23 March, in a 3–2 loss with Huachipato, it was his first goal for Universidad de Chile.