In the middle of the 2011–12 season, Conteras left the club due to the Greek government debt-crisis and opted to return to Colo-Colo, coached by Ivo Basay at the time.

In his country, Pablo is nicknamed Espartaco by Chilevisión relator Paulo Flores specifically, referred him as the Spartan hero of his national team during the matches, when Contreras was under the orders of Claudio Borghi in Chile.

Born in Santiago, Contreras made his way through Colo-Colo's youth ranks, alongside fellow stopper David Henríquez, as the club was then managed by former international – also a defender – Pedro Reyes.

Immediately cast into the Navarrese's starting XI, he made 31 league appearances, but the club could only finish 17th, narrowly avoiding relegation.

He appeared in seven games as Celta eventually lost in the round of 16 to Arsenal, but also saw his team relegate to Segunda División, after a 19th-place finish in the league.

Contreras became first-choice for Celta in the following seasons but, after another relegation, in 2006–07, was deemed surplus to requirements by the coaching staff (Bulgarian Hristo Stoichkov was one of four during the unsuccessful campaign in division two), and left the club in January 2008, after being released from his contract.

Contreras returned to Portugal after four years, joining Braga on a six-month contract,[3] and was regularly used during his spell, helping his team finish seventh.

[5] He made his official debut for the team on 30 August in a 2–0 away win over OFI Crete and his first goal came in an important 1–0 home victory in the derby against Aris.

[11] After the pre-season in Temuco, Contreras played well for his team, now in the Noche Alba against Peruvian side Alianza Lima at the Estadio Monumental.

On 14 April, his assist to Rodrigo Millar for the first goal in the derby against Universidad Católica, salvaged a 1–1 draw at the Estadio Monumental for the first match under new head coach Luis Pérez after Basay's departure, who abandoned the club after a 4–2 away loss against Unión Española.

In 2000, Contreras participated at the 2000 Summer Olympics, where Chile won the bronze medal, and the player was named one of the best defenders in the tournament.

The employees claimed the team players were celebrating drunk, throwing food, and destroying hotel property after qualifying for the second round of the tournament – Chile lost the next game 6–1 against Brazil.

After being reinstated, Contreras became an important member under Marcelo Bielsa, as Chile qualified for the World Cup in South Africa, the nation's first in 12 years.