Díaz began the season as a substitute player replacing to Guillermo Marino in all second halves of a game, but due to his good performances, he ended up replacing Marino on the starting lineup. On 4 June 2011, he scored a wonderful 26-yard free-kick versus O'Higgins, in Universidad de Chile's amazing 7–1 rout for the playoff's semi-final. Following the title obtained in the Apertura Tournament and the departure of Felipe Seymour to Italian Serie A side Genoa, Díaz started to play in Seymour's former position in the starting lineup as a central midfielder, with a more defensive role.
When the Clausura Tournament began, former Universidad de Chile midfielder Manuel Iturra was heavy linked with the club, to replace to Seymour, but Sampaoli decided finally against Iturra and for Díaz, who with the given confidence stepped up his game and became one of the key players of the team. His great performances in the local tournament and in the 2011 Copa Sudamericana caught the eye of national team's coach Claudio Borghi to play in the 2014 World Cup qualifiers. On 19 October, Díaz played in the Copa Sudamericana's round of 16 match against Flamengo. In that match, Universidad de Chile historically beat 4–0 as visitors, something never done by a Chilean team. In the second leg match, Díaz scored the only goal of the game in a 1–0 win at Estadio Nacional, winning the man of the match award. The next game of his club against the rivals, Colo-Colo, and he again was the man of the match in a 2–2 away draw. In that same match, Díaz was punished by the Anfp for obscene gestures to the Garra Blanca, the barra brava of Colo-Colo. After his performances, he was called up by Borghi for play against the Uruguayan national football team at Centenario Stadium for the World Cup qualifiers. On 23 November, for the semi-finals of the Copa Sudamericana against Vasco da Gama, Díaz played in a 1–1 away draw at São Januário Stadium. He played an important role in the match, winning important balls in the middle of the pitch and assisting Osvaldo González, with a free kick to score the equalizing goal in the 79th minute. In the second leg game against the Brazilians, Díaz was named once again the man of the match in a 2–0 win. In the next game against LDU Quito for the first leg final, he made another assist to Eduardo Vargas, who scored the only goal of game. On 14 December, in the final of the tournament, Díaz played a good role in a 3–0 win over LDU, being crowned as the best champion of this tournament. According to the South American media, they compared to Universidad de Chile with Barcelona and Díaz with Xavi. Winning the Clausura Tournament, Universidad de Chile made a successful season earning three titles in one year, with Díaz as one of the key players of the season along with Johnny Herrera, Eduardo Vargas, Marcos González and José Rojas.
Six years after his participation with the U-20 team, on 7 September 2011, Díaz was called up by Claudio Borghi to play in the 2014 World Cup qualification against Uruguay and Paraguay, in place of Carlos Carmona, who was banned for his participation in the scandal of "Bautizazo". On 11 November, Díaz officially debuted for the Chile senior team in a 4–0 away loss at Centenario Stadium, being replaced by Milovan Mirosevic in the 61st minute. Due to his good performances for Universidad de Chile, he was called up for the match against Ghana at PPL Park, in where he played well in a 1–1 draw. He started again the qualifiers against Bolivia and Venezuela, both 2–0 away victories, where Díaz excelled.