Díaz has earned over 60 caps for Chile since his senior debut in 2011, and represented the nation at the 2014 FIFA World Cup as well as the 2015 Copa América, winning the latter while being named in the Team of the tournament.

[2] Díaz has earned the nickname of "South American Xavi", as both of them have a great ball control capabilities and excellent passing skills.

[3] Díaz began his career in Universidad de Chile youth academy, being immediately accepted by Jorge Cabrera, then coach of the club's lower divisions.

Having finished the 2010 season, Díaz had a deal with Huachipato for a loan, but Universidad de Chile's new coach Jorge Sampaoli wanted him to play for his team in 2011 and the player remained in the club.

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.

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.

[23] In that same match, Díaz was punished by the Anfp for obscene gestures to the Garra Blanca, the barra brava of Colo-Colo.[24][25] After his performances, he was called up by Borghi for play against the Uruguay national football team at Centenario Stadium for the World Cup qualifiers.

[26] 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.

On 4 January 2012, the club received a US$1.5 million bid of Argentine Primera División side Newell's Old Boys for Díaz, but the same player rejected the deal, to play the Copa Libertadores, being also retained with pay rise of part of directive.

Díaz started the season of fine form scoring a penalty goal in a 3–1 win over his old club Deportes La Serena in the first game of Universidad de Chile at the Apertura Tournament.

On 25 February, he missed a penalty kick against O'Higgins in a 3–0 loss, that was saved by the adversary's keeper Luis Marín for the fifth week of the Apertura.

After winning the Apertura with Universidad de Chile, Díaz joined the Swiss side Basel in the summer of 2012, on a four-year deal.

Díaz played his club debut on 17 July in the 2–0 away win against Flora Tallinn in the 1st Leg of the second qualifying round to the 2012–13 UEFA Champions League and he received good compliments.

[38] 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.

[40] 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.

[41] At the start of their 2013–14 season, Díaz was a member of the Basel team that won the 2013 Uhrencup, beating Red Star Belgrade in the final.

Gastón Sauro and Giovanni Sio were both sent off as Basel fell to rivals FC Zürich 2–0 in added extra time, after a goalless 90 minutes.

[51] On 1 June 2015, he scored his first goal for the club in its relegation play-off match which took place at the end of the 2014–15 Bundesliga season, against Karlsruher SC.

[59] In January 2005, aged 19, Díaz caught the attention of José Sulantay, who called up the player to play the South American Youth Championship held in Colombia.

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.